31 October 2012

The new website is here!

After months of work, our new website is finally up and running! Check it out at http://www.apogeeinstruments.com . If you're one of our valued partners, return customers, or product distributors, we encourage you to take a look around and see all the new feautures like: our expanded knowledge base, more detailed product information, a new and improved shopping cart, and more.

We hope you find the new site useful and would appreciate any constructive feedback.

26 July 2012

Contest Update

This is a quick update on our contest for the most extreme measurement in honor of the Olympics.  Enter by sending your most extreme measurement using Apogee products to devin.overly@apogeeinstruments.com for a chance to win a $100 credit on Apogee products and services.

Our current most extreme measurements are listed below.   If you have a measurement that beats it, send us an email!

Highest (altitude)
4557 feet; measured at Apogee Instruments headquarters

Deepest (underwater)
2 feet; measured at Apogee Instruments headquarters

61.36 C; measured by a horizontal FOV infrared radiometer (SI-1H1) on 6/28/12 at 1:30 pm at at the University of Arizona’s Maricopa Agricultural Research Center, Maricopa, Arizona

-37.565 C; measured by the SI-111 infrared radiometer on 7/2/11 at 11:00 at a buried ice mass in Garwood Valley of the Dry Valleys of Antarctica 

Farthest North (latitude)
41.7 north; measured at Apogee Instruments headquarters

Farthest South (latitude)
-78.03 south; at a buried ice mass in Garwood Valley of the Dry Valleys of Antarctica 

The contest ends on August 12, 2012.  See the Citius, Altius, Fortius blog post for more details.

25 July 2012

Estimating the Canopy Fraction in your IRR Field of View

A common problem many individuals face when making canopy temperature measurements with an infrared radiometer (IRR) involves estimating the fraction of the field of view that is occupied by canopy (leaves and stems) and soil. This is important in many settings, because plants do not completely cover the ground and the resulting IRR temperature measurement will be a weighted average of canopy components and soil in the IRR field of view. Estimation of field of view occupied by canopy is particularly important early in the growing season when crops are small and a large fraction of soil is viewed. However, knowledge of field of view composition is important in any application where a uniform surface is not being measured due to different surface components. In this case, canopy and soil will typically have different temperatures. The equation to approximate the fraction of IRR field of view occupied by the canopy (fc) is dependent on plant leaf area and is based on the equation to calculate the canopy extinction coefficient for direct beam radiation [1] and is given as:
where LAI is the leaf area index, and K is the extinction coefficient. K is dependent on two additional variables: the leaf angle distribution parameter (X) and the viewing angle (θ) of the IRR (relative to nadir view = 0°), which is chosen by the user. These variables will be described briefly below. For more help planning the viewing angle of your IRR, click here.

Leaf Area Index (LAI): area of leaves per unit area of ground [m2 m-2], which can be expressed as total leaf area or one-sided leaf area. One-sided leaf area (projected area) is half of the total leaf area and is often called hemi-surface area. LAI is typically reported as hemi-surface area per unit ground area, unless the canopy is largely made up of needle-leaf species. In cases where LAI is not directly measured, it is often approximated from canopy height. A few examples from scientific literature are given in the table below.

Crop LAI Equation (where h is in meters)
Clipped Grass [2] = 24 * h
Alfalfa [2] = 5.5 + 1.5 * ln(h)
Corn [3] = exp(1.64 * ln(1.41 * h))
Soybean [3] = exp(2.38 * ln(4.17 * h))

Extinction Coefficient (K): area of shadow cast on a horizontal surface by the canopy divided by the area of leaves in the canopy, or in other words, the average projection of leaves onto a horizontal surface. The following equation can be used to approximate K:

where X is the leaf angle distribution parameter, and θ is the IRR viewing angle [4].

Leaf Angle Distribution Parameter (X): ratio of average projected area of canopy elements on a horizontal surface to projected area on a vertical surface. X defines the distribution of leaf inclination angles in a plant canopy from 0 (horizontal) to 90 degrees (vertical). For plant canopies with more horizontally-oriented leaves, X is greater than one, and for plant canopies with more vertically-oriented leaves, X is less than one. X = 1 is a good approximation for many plant canopies because leaf area is distributed fairly uniformly among all leaf inclination angles. The figure below shows the inclination angle density for three canopies [4]. The larger X, the more horizontal the leaves are. The equation for these distributions is given by Campbell [5].

Additionally, X values for various crops have been estimated as shown in the table below [4].

Crop X Crop X
Ryegrass 0.67-2.47 Cucumber 2.17
Maize 0.76-2.52 Tobacco 1.29-2.22
Rye 0.8-1.27 Potato 1.70-2.47
Wheat 0.96 Horse Bean 1.81-2.17
Barley 1.20 Sunflower 1.81-4.1
Timothy 1.13 White clover 2.47-3.26
Sorghum 1.43 Strawberry 3.03
Lucerne 1.54 Soybean 0.81
Hybrid swede 1.29-1.81 Maize 1.37
Sugar beet 1.46-1.88 J. artichoke 2.16
Rape 1.92-2.13

A simple widget recently created in the IRR product section of the Apogee website can help make the necessary calculations to estimate the fraction of canopy viewed by an IRR. For more information, click here. If you have any questions or comments, feel free to respond to this blog post below.

Adam Del Toro
Mechanical Engineer 

[1] Campbell, G.S. (1986) Extinction coefficients for radiation in plant canopies calculated using an ellipsoidal inclination angle distribution. Agricultural and Forest Meteorology 36:317-321.

[2] Allen, R.G., et al. (2001) The ASCE Standardized Reference Evapotranspiration Equation. Pg B-6. http://www.kimberly.uidaho.edu/water/asceewri/appendix.pdf.

[3] M.C. Anderson, et al. (2004) Upscaling ground observations of vegetation water content, canopy height, and leaf area index during SMEX02 using aircraft and Landsat imagery. Remote Sensing of Environment 92:447-464.

[4] Campbell, G.S. and Norman, J.M. (1998) An Introduction to Environmental Biophysics, 2nd ed. pg 250-253.

5] Campbell, G.S. (1990) Derivation of an angle density function for canopies with ellipsoidal leaf angle distributions. Agricultural and Forest Meteorology 49:173-176.

18 July 2012

Lights, [Sensors], Action!

{Photo from: http://bit.ly/Q5LIMb}
Light is a concept that starts off being really simple to understand as a child, and then slowly grows to be something that is much more than meets the eye (literally).

Being a new hire at Apogee, there are a lot of cool sensors and instruments to get familiar with. They range in form and function, as well as by what they measure and how they're used. What many of them have in common is that they measure electromagnetic radiation.

Refresher course: Everything we see is caused by a small slice of electromagnetic radiation. We see electromagnetic radiation between the wavelengths of about 400 and 700 nm, and our eye perceives the different wavelengths in that range as a rainbow of colors. All the colors we see are called visible light. Shortwave radiation includes everything in that visible range, along with some infrared and ultraviolet wavelengths. All light, whether visible or not, is electromagnetic radiation.

I’m amazed that measuring specific ranges of light can be so informative. Just as humans only see a small portion of all the possible wavelengths, other applications only see or use a specific range as well. Apogee makes sensors that measure certain ranges of radiation that when correctly measured, can be used to infer a great deal about the world around us. As an example, here are a few of our light-measuring products, and some of their possible applications:

  • Ultraviolet sensors - Measures UV radiation in the range of 250 to 400 nm. 
    • Germicide lamps
    • UV blocking materials testing
    • Solar UV monitoring 
  • Quantum sensors - Counts photons in the photosynthetically active range (400 to 700 nm). 
    • Photosynthetic Photon Flux (PPF) measurements (total available photons for photosynthesis)
    • Aquarium lighting optimization 
  • Pyranometers - Measures shortwave radiation between in the range of about 300 to 1100 nm.
    • Evapotranspiration rates
    • Routine meteorological observations on weather stations (statistical data)
    • Solar panel efficiency testing
    • Energy efficient home automation systems
    • Measuring thickness of certain membranes
  • Infrared radiometers - Measures the infrared radiation (temperature) emitted from surfaces.
    • Plant canopy temperature monitoring
    • Surface temperature of water bodies
    • Road temperature for icy condition detection
    • Avalanche forecasting 

At Apogee, we are continually working to improve our existing radiation sensors, as well as develop new products for light measurement. Check back soon for new product announcements. If you are using our sensors for something unique, or if you have a specific idea or request, let us know.

With the right equipment, light can be much more than something we take for granted. Light measurements can be used to improve agricultural processes, increase technological efficiency, and facilitate environmental safety. Making quality sensors is just one way that Apogee is helping the world make better [light] measurements.


Ryan Lindsley

Mechanical Engineer

11 July 2012

What to look for when buying a sensor

This blog is written by one of newest members of the Apogee team. Schuyler Smith is a recent graduate of Utah State University, with his Bachelor of Science. He has taken up the post of Calibration Technician within the Quality Control Calibration Department. 

What to look for when buying a sensor.

 Many first time customers visit our website wondering if our sensors will fit their application. Answering this question is complex because we have many sensors and multiple options for each sensor. I have compiled this list of things to consider in order to customers narrow down their search when shopping for a sensor.

1. What are you trying to measure?
This seems like a counterintuitive question and yet important to consider. For example customer support emails come in with something like, “I am looking for a sensor to measure the amount of photosynthetically active radiation in water/air. Do you have something that will work?” We are then able to direct them to our line of quantum sensors. Knowing what you want to measure is extremely important in finding the most appropriate sensor for the application.

2. Where is the sensor going to be placed?
Customers are often looking for the cheapest product and may not take into account the wear and tear of their application. Be sure to consider the ruggedness and material compatibility of the sensor when considering placing it 20 meters below the surface of the Dead Sea (or wherever your location may be). I might also add at this point that while Apogee sensors are listed at a particular cable length, we would be more than happy to customize the length to your specification (even up to 100’s of meters on some models. Call for details.)

3. How often will I need to recalibrate it?
Many manufacturers provide information on the need to recalibrate their sensors. Some give a specific timeline, while others may just provide expected outputs that can be compared to your own data to determine if a recalibration is necessary. For more information on the recommended recalibrating interval, please see the blog on this topic (reference the blog here).

 4. What other maintenance will the sensor require?
Some sensors require a wipe down or cleaning to remove dust and debris that affect data. Some sensors are designed to be self-cleaning so that water and dirt rinses off of them.

 5. What is the cost of the sensor?
This can be one of the easiest or hardest questions when considering which sensor to get because the cost analysis should go beyond just the sticker price. Does the importance of the data outweigh the monetary cost? Is getting a more expensive sensor with higher accuracy worth the more money for my application? Is the time cost of setting up the sensor included in the cost analysis?

These are just a few points to consider when buying a new sensor. Our team at Apogee is standing by to answer any questions regarding our products and their practicality in your unique application. We can point you in the right direction even if we’re unable to meet your specific application needs.


Schuyler Smith

Calibration Technician

04 July 2012

Independence Day

Happy Independence Day to all our customers in the USA!

Also, check out last week's blog post about our most extreme measurement competition and enter for a $100 prize! 

27 June 2012

Citius, Altius, Fortius

The Olympic Games will be held in London, England this summer and have the motto of Citius, Altius, Fortius or “Swifter, Higher, Stronger.” At Apogee, we strive to design sensors that perform well in rugged environments and would like to sponsor a friendly competition by surveying where individuals have used our sensors.

Prizes will be awarded for the following categories:
  • highest (altitude)
  • deepest (underwater)
  • hottest
  • coldest
  • farthest north (latitude)
  • farthest south (latitude)

The prize for each category is $100 towards equipment or services offered by Apogee Instruments and a write-up on our website highlighting the research being done.

To qualify, the Apogee Instruments sensor must be deployed in a natural environment (no artificial chambers) and record a measurement. To submit your information (or if you have any questions), send an email to devin.overly@apogeeinstruments.com with the value measured, latitude and longitude of the location, day and time the measurement was taken, any environmental data relevant to the contest, and, if possible, pictures of the sensor in action. We will accept submissions through the last day of the Olympics, 12 August 2012. If a winning entry is submitted after that date, we will highlight it on our website but no other prize will be given.



Devin Overly

General Manager

20 June 2012

Light Intensity Measurements for Light Emitting Diodes (LEDs)

I was working late one evening last week when the phone rang. I debated whether to answer it or not, because it was well after standard business hours and I was trying to finish a project, but I decided I needed a break from my computer screen. I picked up the phone and was greeted by a very polite gentleman, likely from somewhere in the southeastern U.S., as evidenced by the drawl and twang in his voice.

This potential customer said he had recently purchased an LED lighting system for his aquarium, but he was having trouble with coral burning. I’m definitely out of my realm of expertise when it comes to coral, but after talking to him about his proposed application of an Apogee quantum meter to measure the intensity of his new LED system, I figured out that the problem was that the light intensity was too high for the coral.

After explaining his desire to measure the intensity of his LED lighting system with a quantum meter, in hopes of achieving the proper light level for his coral, I started to explain how the quantum meter worked. It became clear, however, that he already knew the meter was designed to measure the total number of photons between 400 nm and 700 nm, the photosynthetically active radiation (PAR) range. What he really wanted to know was the accuracy of the quantum meter when used to measure LEDs. Not surprisingly, with the advancement of LED technology in recent years, this is a question frequently asked by customers.

A previous blog post  provided some qualitative information regarding the use of a broadband device (i.e. quantum/PAR sensors or meters) to measure a narrowband radiation source (i.e. many LEDs currently on the market), where it was stated that a spectroradiometer is the best instrument to accurately measure light intensity of LEDs. While this is true, quantum meters can be used to measure LED intensity, and many customers use them for this application. As a result, an estimate of Apogee quantum meter accuracy for measuring LEDs is very practical.

The error associated with a quantum meter (or sensor) measurement of light from a source that has a different spectrum than the source used to calibrate the meter is called spectral error. Spectral error arises because no quantum meters perfectly match the defined quantum response, meaning they do not respond to all wavelengths of light equally between 400 nm and 700 nm. Apogee quantum meters are sensitive to wavelengths between approximately 370 nm and 665 nm, with a relatively flat response between 450 nm and 650 nm due to the blue pigment used in the diffuser (Figure 1). However, they are not equally sensitive to the wavelengths within the photosynthetically active range (Figure 1). In order to determine spectral error, the spectral responses of the quantum meter, calibration light source, and light source to be measured are required, along with some spectra-dependent calculations (for details, see Federer and Tanner, 1966; Ross and Sulev, 2000).

Apogee quantum sensors and meters for electric lighting are calibrated in a custom chamber filled with T5 cool white fluorescent lamps. LEDs have a very different spectral output than T5 lamps (Figures 2, 3, and 4), thus some degree of spectral error is expected. For the narrowband, broadband, and mixed LEDs shown below, spectral errors are 8 % or less. Apogee quantum sensors and meters are less sensitive to blue wavelengths (near 400 nm) compared to longer wavelengths, and thus read low under blue LEDs. Conversely, Apogee quantum sensors and meters are more sensitive to green and red wavelengths (above 500 nm) compared to blue wavelengths, and thus read high under green and red LEDs. The broadband white LEDs output a small proportion of radiation beyond the upper end of the Apogee quantum sensor/meter sensitivity range (665 nm), and thus yield low measurements for the white LEDs.

IMPORTANT NOTE: LEDs that output a large proportion of radiation above approximately 660 nm will read very low and should not be measured with an Apogee quantum sensor/meter.

I did my best to explain, over the phone, the three preceding paragraphs worth of information to the customer. He thanked me for my time, and then ordered a quantum meter the next day. After hanging up the phone following an after-hours tech support call, I was glad to have helped a customer, and even more glad to be inspired by one at the same time.

LED Error [%]
Blue (448 nm peak, 10 nm FWHM) -8.5
Green (524 nm peak, 15 nm FWHM) 8.0
Red (635 nm peak, 10 nm FWHM) 6.9
Cool White -2.0
Neutral White -3.8
Red, Blue Mixture 4.9
Red, Green, Blue Mixture 5.6

Table 1: Theoretical Spectral Errors for Apogee Quantum Meter Measurements of Multiple LED Sources

Figure 1: Apogee quantum sensor/meter response (blue line) compared to defined quantum response (black line) of equal sensitivity at all wavelengths between 400 nm and 700 nm.

Figure 2: T5 cool white fluorescent spectrum (lamp used by Apogee for electric light calibration of quantum meters; black line) compared to narrowband color LEDs (blue, green, red lines) and defined quantum response (gray line).

Figure 3: T5 cool white fluorescent spectrum (lamp used by Apogee for electric light calibration of quantum meters; black line) compared to broadband white LEDs (cool white fluorescent – blue line, neutral white fluorescent – green line, warm white fluorescent – red line) and defined quantum response (gray line).

Figure 4: T5 cool white fluorescent spectrum (lamp used by Apogee for electric light calibration of quantum meters; black line) compared to mixtures of narrowband color LEDs (red/blue – blue line, red/green/blue – red line) and defined quantum response (gray line).

Federer, C.A. and C.B. Tanner, 1966. Sensors for measuring light available for photosynthesis. Ecology 47:654-657.

Ross, J. and M. Sulev, 2000. Sources of errors in measurements of PAR. Agricultural and Forest Meteorology 100:103-125.


Mark Blonquist

Chief Science Officer

13 June 2012

Signal to Noise Ratio

My last blog explained the difference between single-ended and differential measurements. To follow-up, I want to discuss another key concept in the quest to make accurate and consistent measurements: signal to noise ratio (SNR). I will also reiterate the importance of a differential measurement.

Signal to noise ratio is the ratio of the signal voltage to the noise voltage:

SNR = Vout/Vnoise

SNR is usually averaged, and a good SNR is dependent on the measurement being made and desired accuracy of the measurement.

Noise is usually specified as the root mean square amplitude of a voltage (VRMS). Noise can come from multiple sources, including the datalogger, machines, radio frequencies, and power supply lines. The noise inherent in the datalogger can be less than 1 mVRMS, or even 1 µVRMS. Machines, like motors, could introduce noise with amplitudes greater than 1 VRMS. Some dataloggers, such as those made by Campbell Scientific, filter out the power supply noise by filtering out any noise with a frequency of 50/60 Hz, but the machine and radio frequency noise can be more variable, so it can’t be filtered as easily. Sensors with large signals have more “wiggle” room, whereas sensors with µV-scale signals, such as thermocouples and Apogee SI-100 series sensors, will be much more affected by noise.

Noise can be partially filtered out when differential measurements are made because it will cancel itself out. A single-ended measurement doesn’t have the same luxury. Always grounding the shield wire and always using twisted pair wire can also help mitigate noise. The drain wire is connected to a metal shielding around the twisted pair wire and acts as a Faraday cage blocking electric fields. Twisted pair wire is designed to reduce noise by balancing the signal with an equal and opposite signal, which is then cancelled out by taking a differential measurement. A datalogger designed for low voltage, differential measurements can also help make all the difference when it comes to SNR.

Below is a table describing the best way to check for noise on different sensors from Apogee Instruments.

Sensor Method
SI-100 Series Cover the aperture with a small piece of foil and wait for the foil temperature to equilibrate with the sensor temperature. The target temperature should match the sensor body temperature and be stable to within 0.02 C.
SP, SQ, SU Series

MP, MQ, MU Series
Cover the sensor with a cap or dark cloth, so that no light reaches the detector. The reading should be zero and stable to within 1 mV.



Skif Smith

Electrical Engineer

06 June 2012

Reference Pyranometer Traceability and Recalibrations

For most applications, a pyranometer is only as good as its calibration. This makes the initial calibration process, and subsequent recalibrations, critical steps for accurate measurement of solar radiation. The accepted worldwide standard for global solar irradiance is the World Radiometric Reference (WRR), maintained by the World Radiation Center in Davos, Switzerland. The WRR was introduced in 1980 with the intent of bringing congruity to all solar radiation measurements; it has an estimated accuracy of 0.3% [1].

Apogee maintains a group of four ISO (International Organization for Standardization) classified thermopile (black-body) pyranometers as reference standards for global solar radiation. In order to maintain traceability to the WRR, these reference standards are recalibrated every year (alternating two of the four pyranometers each year) by the National Renewable Energy Laboratory (NREL), specifically the Solar Radiation Research Laboratory (SRRL) in Golden, Colorado [2]. This laboratory has become the North American reference standard for solar radiation. A two year recalibration cycle is typically recommended by manufacturers of thermopile pyranometers due to the potential for sensitivity loss over time (the black-body sensor gradually becomes a gray-body). We maintain this highly uniform group of replicate reference instruments (Figures 1 and 2) not only to allow for an accurate calibration of Apogee’s photodiode pyranometers, but also to provide recalibration services for all types of pyranometers, both thermopile and photodiode models.
Figure 1: Measured incoming shortwave radiation by Apogee’s four reference pyranometers near the summer solstice (22-June-2011) in Logan, Utah. Models include Kipp & Zonen CM21, CM11, CMP11 and Hukseflux SR11.

Figure 2: Comparison of Apogee’s four reference pyranometers near the summer solstice (22-June-2011) in Logan, Utah. The reference for comparison is the mean of all four pyranometers and the time axis has been narrowed to show data with zenith angles less than 70° (8:00 am to 7:00 pm).

Our calibration facility is located in Logan, Utah at 41.7° N latitude. All thermopile pyranometers sent in for recalibration are completed outdoors under cloudless sky conditions. We limit these outdoor calibrations from the vernal (spring) equinox to the autumnal (fall) equinox so that calibrations include a greater range of solar intensity levels and sun angles. A photodiode pyranometer is best calibrated to the sun as well, but with a stable set of replicate transfer standards, these pyranometers can be calibrated indoors under a calibration lamp with minimal uncertainty. This allows for rapid turn-around on recalibrations. The transfer standards used for indoor calibrations are calibrated several times each year, between the spring and fall equinox against the four black-body reference standards.

For further information on recalibrations, including pricing, please click the following link: http://www.apogeeinstruments.com/recalibration.html.

Example calibration certificates that accompany each sensor can be viewed below:
Thermopile Pyranometer (Outdoor)
Photodiode Pyranometer (Indoor)

[1] URL: http://www.pmodwrc.ch/pmod.php?topic=wrc

[2] URL: http://www.nrel.gov/solar_radiation/


Jacob Bingham
Customer Support & Technical Manager

30 May 2012

Uniformity, Repeatability, Stability, and Accuracy

Sensor manufacturers often provide information regarding uniformity, repeatability, stability, and accuracy on their specification sheets. But what do they really mean to you, the person making the measurement?

{Image from http://www.freedigitalphotos.net}
Uniformity is a type of systematic error that refers to the consistency of a measured value, either in a spatial distribution or compared to another sensor taking the same measurement. For example, a scientist seeking to know the uniformity of a large set of thermistors (same type and model) could take measurements of a circulating water bath held at a “constant” temperature. The manner in which the thermistors vary in comparison to one another would determine their uniformity.

Repeatability is similar to uniformity except that it deals with how consistent a particular sensor is against itself. It can be used to describe the ability of a sensor to provide the same result, under the same circumstances, over and over again. For instance, infrared radiometers (IRRs) manufactured by Apogee Instruments have a repeatability of 0.05°C (when within calibrated target and sensor body temperature ranges), denoting that measurements made under the same conditions should be within 0.05°C of the mean of those measurements. Repeatability is typically due to random noise, which is often outside of our control.

Stability deals with the degree to which sensor characteristics remain constant over time. Changes in stability, also known as drift, can be due to components aging, decrease in sensitivity of components, and/or a change in the signal to noise ratio, etc. Amplified pyranometers from Apogee Instruments illustrate this concept well with a stability of less than 3% per year. In other words, each year, under normal conditions, one can expect the sensor’s readings to change by less than 3%.

Accuracy, analogous to uncertainty relative to a reference, is in its simplest terms the difference between measured and “true” values. During calibration, measurements are compared to a reference, ISO or NIST traceable where available. Accuracy is determined by performing a general expanded uncertainty analysis, where all of the systematic and random uncertainties are combined using ISO uncertainty standards (which can be a discussion for a different day).

For each of the examples above, we must assume that a large sample size was used, and that the sensors used were chosen at random. Sensor specifications listed for uniformity, repeatability, stability, and accuracy from Apogee Instruments are based on a 95% level of confidence. This means that specifications listed for each sensor are guaranteed for at least 95% of all measurements taken and/or sensors used. Specification sheets for all of our sensors can be found in each of our product sections online. If you have any questions about this blog post, feel free to comment below.

Extra Resources:

Experimentation, Validation, and Uncertainty 
Analysis for Engineers
Third Edition
Coleman, H.W. and Steele, W.G.
John Wiley & Sons, Inc., 2009

Meteorological Measurement Systems 
Brock, F.V. and Richardson, S.J.
Oxford University Press, 2001


Adam Del Toro
Mechanical Engineer

23 May 2012

New Kid on the Blog-k

Apogee Instruments continually strives to develop new and innovative instrumentation, improve existing products, advance sensor applications, streamline current manufacturing processes, and provide immediate and effective customer support, all in an effort to help our customers make better measurements. The lifeblood of this effort, or of any company, is the people doing the work. To expand our capabilities, we are pleased to announce the addition of a new engineer, Ryan Lindsley. We wanted to give Ryan the opportunity to introduce himself. 

I graduated a few weeks ago from Utah State University with a degree in mechanical engineering and a minor in business. While my scholastic educational experience may be at a close, I’m beginning a whole new learning experience as a new mechanical engineer for Apogee Instruments (maybe you’ve heard of them?). While I previously spent most of my time on campus, Apogee is my new home away from home. I’m still learning about this company, but as its newest addition, allow me to share a little about myself.

College was a good experience, but as any engineering student could tell you, it was no picnic. There were plenty of projects and homework assignments to fill my time, but all that work helped me to become more efficient and allowed me to expand my abilities. My last year in school was my favorite. Not only did I have rock climbing in my schedule, but I was also able to take the senior design class. I had always looked forward to that class; an opportunity to get hands-on experience in applying what I had learned. My team built a transformable wheelchair. I did all the modeling and supervised the building phase of the project, both of which were great experiences. I also created a poster for the chair, which summaries the project and explains why such a wheelchair is needed.

While my degree is in mechanical engineering, I don’t view myself as a typical engineer. I don’t particularly enjoy math, but I like solving problems. I took business classes to broaden my knowledge, and to open more doors. I like to work with others and I know the value of teamwork. My inquisitive nature and desire to create solutions led me into engineering, but it is also leading me to learn as much as I can from all areas of study.

Here are some more semi-applicable facts about me, in case you’re curious:

• I’ve been married for almost 3.5 years (feels like 2 max).
• I want to get an MBA. However, because of the high costs associated with attending, those plans have been put on hold.
• I’ve always wanted to own a business. It doesn’t matter if it turns into a big corporation, or if it’s just a small side project.
• A life goal of mine is to invent something. Something awesome.
• I’m published! I was able to write a guest article for SAE Momentum magazine about my thoughts during an internship experience. ("Outside the Classroom." SAE Momentum (2011): 2. Print.)
• I read a lot of tech news to stay up to date on the latest gadgets and inventions.
• My dad (David Lindsley) is an artist. You might even recognize some of his work.

I feel privileged to be able to work with such high caliber people as those here at Apogee. We make some amazing products and while I’ve only been here a short time, I have been able to see the drive and determination in everyone to provide the very best to our customers. I’m eager to learn all I can, and contribute everything I know to this company. Whether it’s modeling parts using Solidworks or crunching some numbers with Matlab, I’m excited to spend my time helping to research and create products that will enable our customers to ‘Make Better Measurements’ of the world around us.


Ryan Lindsley
Mechanical Engineer

16 May 2012

Featured Projects - Solar 4R Schools

Our Featured Project series is a new blog series where we highlight what some of our customers are doing with our products. If you have a project you would like to have included please email us at admin@apogeeinstruments.com

{Photo from www.solar4rschools.org}
About a year ago, we were contacted by one of our customers to answer some technical questions about our pyranometer sensors. We talked to Craig Collins from Bonneville Environmental Foundation (http://www.b-e-f.org/) about a project they had developed called Solar 4R Schools (http://www.solar4rschools.org). The program works to put renewable energy technology in school buildings throughout the United States. The technology gives students a chance to learn about renewable energy as well as providing the schools with electricity.

Bonneville Environmental Foundation was founded in 1998, with a mission of “bridging the gap between different ideologies, the opposing views of political parties, environmental and business leaders to define common ground and solutions to our energy and water issues”. They work to “find innovative, high-impact solutions to some of the nations most pressing energy, carbon and freshwater challenges” (http://www.b-e-f.org/meet).

{Photo from www.solar4rschools.org}
Solar 4R Schools was founded in 2002 and has installed more than 100 photovoltaic systems for schools and community centers. It has also introduced more than 40,000 students to renewable solar energy. Through their outreach, they plan to educate more than just students. They hope to show parents, teachers, school administrators, city officials and even the installing contractors that solar energy is safe and reliable and can be a viable energy source for more than just schools.

Solar 4R Schools uses our SP-110 pyranometer and our free tool the ClearSky Calculator to monitor the solar panels they install in schools. The “About” page on Solar4RSchools.org says, “Solar 4R Schools educates students, teachers and community members about the science and benefits of renewable energy technology. The program provides hands-on activity guides, science kits and demonstration solar electric systems at no cost to schools, by working with local funding partners who want to show their commitment to renewable energy education. To receive a solar-electric system, schools must agree to own and maintain the system after installation. In turn, the school receives an exciting learning tool and all of the clean, renewable electricity it produces.“

Liberty High School in Renton, Washington features a solar panel with a dual-axis tracker and an Apogee SP-110 pyranometer. Solar 4R Schools is working on a new website feature called the Data Exploration Center where guests and students can see and share project data.

 At Apogee our ongoing goals include a commitment to creating innovative instrumentation for measuring climate change, improving sustainable food production and developing renewable energy. We are proud to have our sensors included in this great program. For more information about Solar 4R Schools, or to apply for a project at your school, please visit www.solar4rschools.org.

Whitney Mortensen
Marketing & Graphic Design

09 May 2012

Energy Benefits of Highly Reflective Rooftops

Ten years ago I began building my own home in Nibley, Utah. When it came time to pick the color for the asphalt shingles I talked my wife into a light gray color, compromising aesthetics in lieu of performance. Although I didn’t have any data to back it up, I knew that a lighter roof would heat up less from solar radiation, reducing the need to cool the house in the summer. I rationalized that in Cache Valley, the roof is covered with snow most of the winter and so the benefit of a dark roof helping to heat the house would be minimized in that regard. I never measured the temperature of my roof, but I knew the light color made a difference because our house stayed cool while running our swamp cooler less often than our neighbors. Now that I am at Apogee, my understanding of albedo far surpasses what I knew then, and I could measure roof temperature with an infrared sensor to confirm the benefit of a light-colored roof.

My interest in the subject of high-albedo roofs was piqued when one of our customers forwarded me a copy of a paper (Gaffin et al., 2012 – see full citation below) they recently published. To partially mitigate the urban heat island effect, roofs with a high albedo membrane, such as EPDM (ethylene—propylene—diene monomer) and TPO (thermoplastic polyolefin), are used in new construction. Much of the study compared the difference in surface temperatures between black and white surfaces composed of the various roofing materials previously mentioned. The customer used an Apogee infrared radiometer to measure rooftop membrane temperature in New York City. For the TPO test case, a black geotextile cloth sample was used to compare against the white membrane. Peak temperature differences reached as high as 23.7 oC with average daily temperature differences equaling 6.6 oC. All surfaces had comparable initial albedos, with the white acrylic paint experiencing a considerable decline in albedo over time. Location is another significant factor. The acrylic paint site was possibly affected by a large traffic artery adjacent to the test site building, as well as an above ground subway line. Another site was affected by leaf litter and vegetation debris from surrounding trees.

When our current building for Apogee Instruments was constructed, a 60 mil TPO membrane was used. Historically, urban roofs have been asphaltic to allow for varying roof geometries, as well as the need for numerous roof structures such as heating and cooling units, ducts and vents. These asphaltic membrane roofs are typically topped with sand, gravel or rock and have low albedos. Gaffin et al. (2012) also looked at a white elastomeric acrylic paint that has been developed to apply to asphaltic membranes and is being used by New York City’s government for an albedo enhancement program. The white acrylic paint does significantly increase the albedo of the existing roof materials but the decrease over time indicates that all new construction should use EPDM or TPO membranes. Additionally, low emissivity may be a benefit in colder climates and this parameter should be considered in future performance standards.

I found the article very interesting and was surprised at the peak temperature differences demonstrated with different colors of the same material. It was validation for me of the choice to use a light gray shingle color when building my house. I was also pleased to see that when Apogee built our building, the materials selected help minimize heat gain, and in turn make the building more environmentally friendly. I appreciate working for a company that has a commitment to environmental responsibility and that builds sensors to promote research into renewable energy and green building practices.

Gaffin, S.R., M. Imhoff, C. Rosenzweig, R. Khanbilvardi, A. Pasqualini, A.Y.Y. Kong, D. Grillo, A. Freed, D. Hillel, and E. Hartung, 2012. Bright is the new black – multi-year performance of high-albedo roofs in an urban climate. Environmental Research Letters 7:014029 doi: 10.1088/1748-9326/7/1/014029.


Devin Overly
General Manager

02 May 2012

Revisiting the Clear Sky Calculator

I usually spend every other Saturday in my hometown, working as a butcher in my Dad and Uncle’s grocery store. Last time I was there, during an afternoon lull, I noticed a calibration verification sticker on the scale used to weigh meat (not unlike the verification stickers found on gas pumps). Accurate calibration of the meat scale is required to ensure that the customer gets what they are paying for, and to ensure my Dad and Uncle are making a reasonable profit on goods being sold. I’ve never been around to witness the USDA inspector verify the calibration of the scale, but I can imagine he or she carries a small set of reference weights that are placed on the scale to determine the scale accuracy and need for recalibration.

Customers often contact Apogee Instruments to inquire about how often pyranometers and quantum sensors should be recalibrated. While it is safe practice to follow the general recommendation to recalibrate radiation sensors every two years, it may not be necessary to recalibrate on a fixed schedule if a sensor consistently matches a reference. The challenge for many pyranometer and quantum sensor users is they don’t have a handy reference, something analogous to weights that can be placed on a meat scale.

In response to customer inquiries regarding recalibration requirements, in 2009 Apogee Instruments developed the Clear Sky Calculator (www.clearskycalculator.com), an online tool that can be used to estimate the intensity of solar radiation (either total global shortwave radiation, measured by pyranometers, or global photosynthetic photon flux density, measured by quantum sensors) incident on a horizontal surface at any time of the day, at any location in the world. The equations used to estimate clear sky solar radiation with the Clear Sky Calculator come from the clear sky solar radiation model used to calculate net radiation in the ASCE Standardized Reference Evapotranspiration Equation (http://www.kimberly.uidaho.edu/water/asceewri/index.html). The only input requirements to the calculator are site elevation, latitude, longitude, reference longitude, and air temperature and relative humidity measurements or estimates. These data are typically easy to obtain, making the Clear Sky Calculator a simple solar radiation reference that can be used to estimate pyranometer and quantum sensor accuracy and determine the need for recalibration.

When used near solar noon over multiple clear, unpolluted days during spring and summer months, accuracy of the Clear Sky Calculator is estimated to be ± 4 % in all climates and locations around the world. As an example, modeled incoming shortwave radiation (SWi) from the Clear Sky Calculator closely tracked measured SWi (data from a heated and ventilated Kipp & Zonen CM21 pyranometer) for a clear day (April 21, 2012) in Logan, Utah (Figure 1). The ratio of measured SWi to modeled SWi was between 1.00 and 1.05 (0 % and 5 %) from 9 AM to 6 PM (solar zenith angles less than 65°) (Figure 2). The average ratio from two hours before solar noon to two hours after solar noon was 1.02 ± 0.01 (2 ± 1 %). A more detailed discussion of Clear Sky Calculator accuracy is given on the webpage (http://clearskycalculator.com/model_accuracy.htm), where the necessary accuracy of the required inputs is discussed.

Apogee strongly encourages our customers to use the Clear Sky Calculator as an effective way to monitor pyranometer and quantum sensor performance and determine the need for sensor recalibration. If a sensor is consistently different from the Clear Sky Calculator by more than a few percent, please contact us about recalibration.

Figure 1: Comparison of measured incoming shortwave radiation (SWi) (red line) and modeled SWi on April 21, 2012 in Logan, Utah. Measured SWi is from a heated and ventilated blackbody pyranometer (Kipp & Zonen model CM21). Modeled SWi is from the Clear Sky Calculator.

Figure 2: Ratio of measured shortwave radiation (SWi) to modeled SWi over the course of a clear day (April 21, 2012) in Logan, Utah. Mean ratio = 1.02 ± 0.01 (2 ± 1 %) for measurements averaged from two hours before solar noon to two hours after solar noon (solar noon occurred at approximately 13.5). The dip in the morning near 7 is due to mountains on the east side of the valley where Logan is located.


Mark Blonquist
Chief Science Officer

25 April 2012

Differential vs. Single-ended Measurements

Apogee SO series oxygen sensor
A couple of years ago, while talking to a customer who had a limited number of input channels on his datalogger, I suggested measuring an oxygen sensor using a single-ended channel instead of a differential channel. He questioned the suggestion, thinking that a differential signal can only be measured using a differential channel. I used this opportunity to educate him about the difference between differential and single-ended measurements. An oxygen sensor can indeed be measured using a single-ended channel, by wiring the low output of the sensor to ground rather than the low input on the differential channel, but there are some trade-offs. This blog post outlines the trade-offs between single-ended and differential measurements, and describes when differential is necessary and when single-ended can be used.

A differential voltage is “floating”, meaning that it has no reference to ground. The measurement is taken as the voltage difference between the two wires. The main benefit of a differential measurement is noise rejection, because the noise is added to both wires and can then be filtered out by the common mode rejection of the data acquisition system. Differential measurements should be used if the sensor is in a noisy environment or for sensors with output voltages susceptible to noise interference. For example, we recommend that the thermopile output from Apogee SI-100 series infrared radiometers should always be measured differentially because the small voltages are susceptible to noise.

A single-ended measurement is taken as the voltage difference between a wire and ground. The noise is only on the positive wire, and as a result, it is still measured along with the output voltage from the sensor. Some sensors, for example amplified versions of Apogee SP and SQ series sensors, only have a single output and must be wired into a single-ended channel. A sensor with a differential output can be wired for single-ended by wiring the low side to ground. This is usually done to reduce the number of channels needed to measure the sensors. It should be noted that some sensors (for example, the thermopile output from Apogee SI-100 series infrared radiometers) can output a negative voltage which means that the data acquisition system needs to be able to measure negative voltages.

It should also be noted that taking a single-ended vs. differential measurement might also be based on the data acquisition system or the cabling. Shielded twisted-pair cable is also very effective at reducing noise in the signal other types of cable might not have the same effect. The data acquisition system is also important to consider if it doesn’t have a very uniform ground the signal could be biased. In most cases, modern data acquisition systems have improved in this area and it isn’t as much of a concern.

It should be stated that differential measurements should always be used if there are enough available datalogger channels or if the data acquisition system cannot measure negative voltages. Table 1 (below) shows which measurement method should be used with specific Apogee Instruments sensors. Again, it should be remembered that any in the differential measurement column can be measured single-ended if the conditions warrant it.

Table 1: Apogee Instruments Sensors Output
Differential Single-ended
SI-100 series - thermopile
(single-ended measurement strongly discouraged)
SI-100 series - sensor body temperature
SP-100 series SP-200 series
SO-100/200 series SF-110
SQ-100/300 series SQ-200 series
SU-100 ST-100



Skif Smith
Electrical Engineer

18 April 2012

New Product: Radiation Frost Detection Sensor (SF-110)

At the beginning of each growing season, as leaves and buds begin to emerge, crops will be susceptible to frost damage. On clear, calm nights, leaf and bud temperature can drop below freezing even if air temperature remains slightly above 0 °C (see Figure 1 below). This is called a radiation frost and is due to the lack of air mixing (wind) near the surface, and a negative net longwave radiation balance at the surface (more longwave radiation is being emitted from the surface than what the surface is absorbing from the clear sky). Under cloudy and/or windy conditions, radiation frost events do not occur.

Growers have options for mitigating damage caused by radiation frost, for example, heaters and wind machines to heat and mix the air within the crop canopy. Although these preventative measures are effective, they are also expensive to operate, requiring significant amounts of fuel and/or electricity. Historically, growers have depended on air temperature measurements and weather forecasting to determine the need to initiate frost protection measures. Air temperature can be misleading because the same atmospheric conditions that cause radiation frost also cause crop temperature to drop below air temperature, but not always by the same amount [1]. Forecasting requires use of a surface energy balance model with multiple measurement inputs [2] [3]. An estimate of crop temperature, based on a direct temperature measurement, is a simpler, more straightforward method of accurately determining when crop temperatures drop below the freezing point.

Apogee Instruments is pleased to announce the release of our radiation frost detection sensor, the SF-110. The SF-110 is a combination of two temperature sensors (precision thermistors) in a single housing. One sensor is designed to mimic a plant leaf and the other a flower bud. The SF-110 provides close approximations to leaf and bud temperatures and can be used for prediction of frost on leaves and buds.
The temperature measurement range of the SF-110 is -40 to +70 °C with an accuracy of ± 0.1 °C from 0 to +70 °C. However, the sensor is intended for applications in cropped fields and orchards when temperatures will be near freezing, and where air temperature measurements are not a good predictor of frost formation (Figure 1). The SF-110 offers a simple and effective method of helping growers determine when to initiate expensive frost protection measures, thereby saving crops in addition to operating costs. For more information on the SF-110 please click here.

Figure 1: Leaf and bud temperature approximations measured with an Apogee SF-110 compared to air temperature (top panel) and wind speed (bottom panel) on the evening of October 26, 2011. Leaf and bud temperatures were both below air temperature after 6 PM (hour 18) and reached the freezing point well before the air.

[1] “Frost/Freeze Protection for Horticulture Crops”, URL: http://www.ces.ncsu.edu/depts/hort/hil/hil-705.html 

[2] Kala, J., T.J. Lyons, I.J. Foster, U.S. Nair, 2009. Validation of a simple steady-state forecast of minimum nocturnal temperatures. Journal of Applied Meteorology and Climatology 48:624-633.

[3] Lhomme, J.P. and L. Guilioni, 2004. A simple model for minimum crop temperature forecasting during nocturnal cooling. Agricultural and Forest Meteorology 123:55-68.


Jacob Bingham
Customer Support and Technical Manager

11 April 2012

New Product: Horizontal FOV Infrared Radiometer (SI-1H1)

Apogee Instruments is pleased to announce the release of our horizontal field of view (FOV) infrared radiometer (IRR). Some of the features and uses are listed below.


The SI-1H1 IRR is different from any other IRR that Apogee has manufactured in the past. It was designed with a unique rectangular FOV, intended specifically for far-field applications. Unlike previous IRRs, the SI-1H1 has two different half angles: 32° horizontal and 13° vertical; which will be described in more detail below. The sensor has an accuracy of ± 0.2 °C just as the SI-111 and SI-121 IRRs.

Field of View (FOV) 

Field of view (FOV) is typically reported as half-angle. Previously, all Apogee IRRs had an axisymmetric FOV, which depended on the model number. For example, the half angles for the SI-111, SI-121, and SI-131 are 22°, 18°, and 14°, respectively. As seen in the photo above, the SI-1H1 sensor has a rectangular aperture, creating an asymmetric FOV, with a horizontal 32° half angle for the lateral direction of the rectangular geometry and a vertical 13° half angle for the narrower dimension of the rectangular aperture. The figure below demonstrates these two different FOVs (full angle) from cross-sections of the SI-1H1 sensor.

Better Measurements 

The question arises: Why a rectangular slit instead of the usual circular aperture? When using an IRR, one must make sure that only the desired target is in the FOV, in order to make an accurate temperature measurement. For example, a problem some crop scientists face is accidentally having more than their crops in the FOV of the IRR. This could include the sky and/or other background objects (see figure below). Unfavorable images caught in the FOV of the IRR alter the desired temperature measurements and yield incorrect results. By adding a horizontal “filter”, the likelihood of capturing the background is dramatically reduced in certain applications. As expected, the aperture has baffles in order to deter reflected radiation from influencing measurements. Furthermore, the IRR can be mounted at greater angles of inclination from the ground. The SI-1H1 isn’t limited to cropped fields, since unique circumstances could require its use in many applications. In order to calculate the target area (based on the installation directions given below), please click here for a preconfigured Excel spreadsheet.

Installation in the Field 

With the horizontal aspect of this sensor, installation is critical and involves more than mounting the sensor at the correct inclination angle. We recommend the AM-210 Mounting Bracket which allows users to adjust the angle of the sensor with respect to the target area. The AM-210 accommodates the radiation shield designed for all Apogee infrared sensors.

Once the desired angle has been set, the sensor needs to be rotated along its main axis so that the rectangular portion of the sensor is aligned to the horizon. This orientation will minimize the likelihood of capturing sky or other background interference.

If you are not using the radiation shield or the AM-210 mounting bracket, the SI-1H1 has the standard mounting hole (¼ - 20), which is aligned with the horizontal aperture. If the sensor is installed against a completely flat vertical surface, using the mounting hole, the rectangular aperture will be aligned with the horizon.

Apogee is proud to offer another great product to our customers. We are continually focused on product innovation so you can “Make Better Measurements.” To learn more about the new SI-1H1 sensor or to place an order, click here.


Adam Del Toro

Mechanical Engineer

04 April 2012

Better Know a Distributor - Conviron

The ‘Better Know a Distributor’ series highlights other companies that distribute and resell Apogee products. 

Conviron has been in business for almost fifty years and is known worldwide for its quality service and products. The following excerpt is Conviron’s company profile:

Established in 1964, Conviron is the world leader in the design, manufacture and installation of controlled environment systems for plant growth research. Headquartered in Winnipeg, Canada, Conviron employs a global sales, distribution, and service network. Our products can be found in more than 80 countries worldwide, with projects ranging from single-chamber installations to large-scale, multi-chamber plant growth facilities designed and supplied entirely by Conviron. Our innovative design and manufacturing expertise has established Conviron as the industry leader with products that are proven, reliable and robust. As an ISO 9001 company, our products meet universally recognized quality and safety standards. 

As a fully integrated supplier of controlled environment systems, our services encompass the entire project life-cycle - from project consultation to manufacturing, installation, commissioning, and on-going maintenance and service. Our specialized equipment includes reach-in chambers, walk-in rooms and research greenhouses that precisely control light, temperature, humidity, carbon dioxide and other gases, as well as other environmental conditions. With a staff that includes a highly qualified design group of specially trained engineers, technicians and controls experts, Conviron is well equipped to supply both standard and custom applications for our clients.

Conviron has utilized Apogee quantum sensors in their cutting-edge environmental growth chambers for nearly 12 years. Throughout that time, Conviron has not only provided Apogee with a high level of independent validation of our quantum sensors, but they have also acted as an indicator for when certain lighting technologies start to become obsolete while others take hold of market demands. An example of this comes from a couple of years back when Conviron had made the switch from using T12 cool white fluorescent lighting in their growth chambers to the more efficient T5 lamps. This led to the question of whether we could supply our quantum sensor with an electric calibration under T5's rather than our standard T12 calibration. After favorable testing and data comparison with Conviron, we ultimately made a system-wide changeover to T5's for all of our electric calibration quantum sensors. It was later announced that the magnetic ballasts used in many T12 fixtures would no longer be produced for commercial or industrial applications, and as of July 2012 many T12 lamps will be phased out of production completely.

Apogee is happy to work with a knowledgeable and progressive company like Conviron. We are proud of our products used in Conviron chambers and we are proud of the contribution they make to science and research across the globe. For more information about Conviron’s products you may visit their website at: www.conviron.com.


Jacob Bingham
Customer Support and Technical Manager