SOW AERONET Sun Photometer Procurement Contract_PG_JK.pdf

AERONET Sun Photometer Procurement Contract

Description of Sun Photometer and Components

STATEMENT OF WORK

March 23, 2026

TABLE OF CONTENTS

SUMMARY

1. General Description

2. Instrument Specifications

Capabilities

2A – Non Required specification items (These items are part of the specifications but will not be ordered)

• 2-1 Sun and Sky Measurement Mode Selections

• 2-2 Automatic Selection of Geometrical Conditions

• 2-3 Optics

• 2-4 Detectors

• 2-5 Filters

2B – REQUIRED SPECIFIATION ITEMS

• 2-1 Advanced Control Box

• 2-2 Tracking Robot

• 2-3 Microprocessor

• 2-4 DCS Compatibility

• 2-5 Instrument Sensitivity

• 2-6 Power Requirements

• 2-7 Environmental Requirements

3. Description of Daily Measurement Program

• 3-1 Optical Thickness and Water

• 3-2 Langley Plot

3-3 Sky Radiance Measurement

• 3-3.1 Almucantar

• 3-3.2 Principal Plane Measurement

• 3-3.3 Hybrid Scan Measurement

Summary

NASA owns and or manages over 600 Cimel Sun-Sky-Lunar Scanning photometers as part of the EOS Aerosol Validation Program called AERONET. The program is part of a larger Federated Global Network of identical instruments designed to measure aerosol properties from land and ocean sites. In order to ensure compatibility within the network, any additional instruments must be identical in optical characteristics, measurement protocol, data acquisition and field hardness.

The CE 318 T Sun photometer functions reliably in the harsh environmental conditions (humidity, rain, insects, dust and sea spray.)

expected in our remote sites. The instrument is required to have multiple data communication options including the data collection system (DCS) of the international constellation of geostationary meteorological satellites, cellular and PC/internet.

The measurement protocol requires direct solar and lunar plus diffuse sky measurements to be automatically taken according to reprogrammed solar zenith angles and scattering angles optimized for analysis of data to estimated aerosol properties.

We are adding additional systems to the AERONET program. The additional systems being procured for the AERONET program must be identical in function and be electronically compatible with the existing instruments.

Sun and sky-scanning spectral radiometers are used in the AERONET program to monitor aerosol optical properties and precipitable water in near real-time for the validation of satellite-derived retrievals of aerosol properties and provide a uniform database for long-term characterization of aerosol optical properties within NASA's Earth Science program. To develop such a database, AERONET has imposed a standardization in data measurement, data collection, data format, and data processing that is fundamental to the objectives and success of the program. Any deviation from these standards will erode the quality control necessary for network operations. The following instrument specifications are required to meet the requirements of the AERONET network measurement program.

1. GENERAL DESCRIPTION

The radiometer system will measure both sun and lunar irradiances and sky radiances using a combination of spectral filters and a fully-autonomous azimuth/zenith viewing microprocessor-controlled robot. The daily data stream will be transmitted via the internationally-standardized Data Collection System (DCS) aboard the geostationary satellite system GOES, METEOSAT and HIMAWARI. The radiometer must be capable of unattended operation for up to eight weeks in any environmental conditions and be powered by rechargeable batteries and a five watt solar panel.

Place of Performance

Radiometers to be built at the Contractor facility and sent to NASA Goddard Space Flight Center. CIMEL Electronique,172 Rue de Charonne, 75011 Paris, FR

Period of Performance

Oct 1 2026 to Sept 30 2031

2. INSTRUMENT SPECIFICATIONS

CAPABILITIES

The Sun and Sky radiometers must have a broad spectral range from the UV to the short wave infrared. It shall incorporate the digital electronics in the sensor head, and its components are compatible with earlier models of the CE318 including the robots.

The instrument shall incorporate polarization to the standard measurements. It will be an important instrument for new research activities and synergism with future satellite validation activities. It shall be fully compatible with existing system components and network standardization.

The instrument shall be able to take the atmospheric and ocean radiances.

It shall be fully compatible with the existing network components.

The instrument shall be able to be used to extend measurement from daylight only to day and night time measurements with lunar observations in addition to solar observations and support validation of all Earth viewing satellite monitoring systems. It shall be compatible with the existing robot infrastructure.

A. NON REQUIRED SPECIFICATION ITEMS

2.1 SUN AND SKY MEASUREMENT MODE

SELECTION

The radiometer must automatically change gains from the sky radiance measurement mode to the sun-measuring mode without saturating the signal response. It is fundamental that a two-detector two-collimator system be used in order to assess the quality of data from each detector system.

2.2 AUTOMATIC SELECTION OF GEOMETRICAL

CONDITIONS

The automatic instrument is set up on an axis which is able through step-by-step motors to move in two directions, in the zenith and in the azimuth planes. The step-by-step motors piloted by the microprocessor card are able to reach any geometrical conditions. Computations of the equation of Sun are performed by the microprocessor and combined with a four-quadrant detector system enables accuracy of sun position to ±0.05°. Therefore, the specification of accuracy in pointing to any direction is ±0.05, relative to the sun.

2.3 OPTICS

Collimator Detector Sun, 1.2 degree FOV, no optics sky, collimator 1.2 degree FOV, lens required, 10-6 stray light rejection relative to Sun at 2 degrees from Sun.

2.4 DETECTORS

Four quadrant silicon detector for sun tracking, silicon detector for sun and sky radiance for 0.25 - 1.1 micron range. An InGaAs detector is used for 1020 and 1640 nm wavelengths with the second collimator. Detector temperature is monitored from -40 to 60°C at 0.1° C resolution.

2.5 FILTERS

Center band bandwidth in nm: 340/2, 380/4, 440/10, 675/10, 870/10, 500/10, 940/10, 1020/10 and 1640/25 for the CE318T- N and 400/10, 412/10, 443/10, 490/10, 510/10, 560/10, 620/10, 667/10, 779/10, 865/10, 940/10, 1020/10 for the model CE318 T-OC. All filters must be on assisted deposition interference filters. The nominal filter thickness is 3.1 mm.

B. REQUIRED SPECIFICATION ITEMS (To be ordered)

2.1 ADVANCED CONTROL BOX

Must have programmable capability, advanced instrument control including micro stepping robot control, advanced communication options and 32 gigabyte SD card.

2.2 TRACKING ROBOT

The instrument must have 360 zenith and azimuth capability. A full rotation must be completed in 20 seconds. Pointing capability must be fully programmable with options for ground and sky viewing measurements.

2.3 MICROPROCESSOR

The microprocessor shall be housed in a sealed control box.

The microprocessor shall control all pointing, filter wheel rotation, data storage, preprocessing, and data transmission. The microprocessor must be 32-bit capacity. The unit must be solar-and battery-powered and operate unattended for up to a year with weekly maintenance. Data will be stored in Flash memory, SD card and dumped to the DCS system, cellular or PC/internet.

2.4 COMMUNICATION COMPATIBILITY

The spectral radiometer must be compatible with the NOAA/NESDIS Data Collection System (DCS) and the commercially available data collection platforms used to transmit these data through the DCS. The system must be compatible with cellular networks worldwide.

2.5 INSTRUMENT SENSITIVITY

The SNR must exceed 10,000/1 for all channels.

2.6 POWER REQUIREMENTS

The instrument shall be run from battery power and be charged from 5-watt solar panels.

2.7 ENVIRONMENTAL REQUIREMENTS

The instrument shall be sealed from rain, humidity, dust and smoke, and successfully operate within a temperature range of -20 to 50 degrees C for a year with minimum maintenance.

2.8 REPLACEMENT PARTS

1. Sensor head card

2. 4 quadrant detector

3. achromatic front lens

4. polarized filter wheel with polarizers mounted

5. Friction pad for filter wheel

6. Filters

7. Collimator

8. Collimator rod & knob

9. Sensor head cord (3m & 12m long)

10. CPU card with or w/o modem

11. Modem

12. Terminal block

13. Mobile phone - Internal cord

14. GPS - Internal cord

15. Robot strap hook

16. Inserted foot for robot base plate

17. Adjustable foot for robot base plate

18. Fixed foot for robot base plate

19. Flange bearing D3x8

20. Latch assembly

21. Gear reducer motor assembly CE318

22. Mechanical microswitch assembly (with or w/o microswitch)

3. DESCRIPTION OF DAILY MEASUREMENT

PROGRAM

3.1 OPTICAL THICKNESS + WATER VAPOR CONTENT

DESCRIPTION.

Measurement of direct solar irradiance with a calibrated instrument can be utilized to derive atmospheric optical thickness at eight wavelengths, and water vapor using the differential gaseous absorption approach. These measurements will be made with a collimator having a nominal 1.2 degree field of view with no optics.

FREQUENCY: Programmable from 3 to 60 minute measurement interval per hour, both before and after almucantar, hybrid and principal plane observations.

NUMBER OF CHANNELS: 9 Channels (center band l bandwidth in nm):

340/2, 380/4, 440/10, 675/10, 870/10, 500/10, 940/10, 1020/10 and 1640/25.

TIMING: From morning optical airmass 7 to evening optical airmass 7.

3.2 LANGLEY PLOT

The Langley technique consists of performing direct solar irradiance measurements at different air masses. Assuming aerosol optical depth is invariant between airmass 7 and 2, the linear regression of the logarithm of measurement voltages versus air mass gives as an intercept the logarithm of exo-atmospheric voltage and as slope total optical thickness. Accordingly, the value of solar zenith angle will be: 60.0° ,66.4°,70.5° ,73.4°,75.5°, 77.2°, 78.5°,79.5°, 80.4°, 81.2°, 81. 8°, 82.3°, 82.8°)

FREQUENCY: Twice daily

NUMBER OF CHANNELS: 9 (All channels; see above and section 2.5)

TIMING: At during morning and afternoon airmass range

DEDUCED PARAMETERS: Intercept (b), Slope (a), Regression coefficient of natural logarithm of measured signal versus air mass (l/Il s)(r).

3.3 SKY RADIANCE MEASUREMENT

These measurements are made with the full 32 bits microprocessor affording sufficient dynamic range for direct sky radiance spectral measurements from 380 to 1640 nm.

3.3.1 ALMUCANTAR

The almucantar technique consists of measuring the sky radiance in aerosol channels in the azimuth plane with a zenith angle of view equal to the zenith solar angle (8s=8v). The particular geometry (~s=~v) in the measurement of direct solar irradiance is not part of the data set. The step in azimuth Li<D varies with the value of ~s=~v: it is smaller (2°) when ~s=~v is <20° to 0., and incrementally larger as ~s=~v approaches 180° (See table below). Logically, Li<D should also vary according to 85 : the extreme case is 85=0° (sun at nadir) where almucantar measurement is impossible. The table below considers the set of ~s-~v for sky radiance measurement independently of the 8s value. The viewing sequence is as follows:

VIEWING STEP

INCREMENT

NR.

OBS

-6 °,-5.0 °,-4 ° 1.0° 3 -3.5 °,-3 °,-2.5 0,_2 °,00,2 °,2.5°,3 °,3.5 ° 0.5° 8 4°,5°,6,°7°,8° 1.0° 5 10 °,12 °,14 °,16 °,18 °,20 ° 2.0° 6 25°,30° ,35 °,40°,45 °,50° 5.0° 6 60°,70°,80°,90°,100° 10° 5 120°,140°,160° ,180°,200°,220° ,240° 20° 7 260° ,270° ,280° ,290° ,300° 10° 5 310°,315 °,320°,325 °,330°,335 ° 5° 6 340°,342 °,344 °,346° ,348° ,350° 2° 6 352 °,353 °,354 °,355 °,356 ° 1° 5

357.5 °,357.0° ,358.5 °,358.0°,0°,2 °,2.5 °,3 °,3.5 ° 0.5° 8 4°,5°,6° 1° 3

NOTE: The above sequence should be at a single filter position to minimize the acquisition time. The sequence acquisition time should not exceed 30 seconds. The sequence begins by aligning on the sun, to 6 degrees, then sweeping through the sun in the above-stated increments. Upon completion, the filter is changed, alignment is made on the sun, and a new sequence begun. Sun observations precede the almucantar sequence. The principal plane observations immediately follow.

FREQUENCY: 6 times daily

NUMBER OF CHANNELS: 4 (440.0 nm, 670. nm, 870. nm, 1019. nm, 1640 nm)

TIMING: 8h, 9h, 15h, 16h (Local Time)

3.3.2 PRINCIPAL PLANE MEASUREMENT

The sky radiance in the aerosol channels is also measured in the principal plane, that is, the zenith angle will be changed while the azimuth angle is constant. Relative to the sun position, data will be collected according to the following angles: -6, -6, -5, -4, -3.5, -3, 2.5, -2.0, 2, 2.5, 3.,

3. 5, 4, 5, 6, 6,8, 10, 12, 16, 20, 25K, 30K, 35K, 40K, 60, 90, 120.

FREQUENCY: 6 times daily

NUMBER OF CHANNELS: 4 (440.0 nm, 670. nm, 870. nm, 1019. nm, 1640 nm)

TIMING: 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h (Local Time)

3.3.3 HYBRID SCAN MEASUREMENT

This scan incorporates elements of the almucantar and PP scans to maximize the scattering angle necessary for accurate aerosol property retrievals

FREQUENCY: Hourly throughout the day.

NUMBER OF CHANNELS:

7 (380 nm, 440 nm, 500 nm, 670 nm, 870 nm, 1020 nm, 1640 nm)