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aats on plane
The AATS mounted on top of aircraft


Ames Airborne Tracking Sunphotometer

The AATS-14 measures solar-beam transmission at 14 discrete wavelengths from 354-2139 nm, yielding aerosol optical depth (AOD) at 13 wavelengths and water vapor column content. Azimuth and elevation motors controlled by differential sun sensors rotate the tracking head, keeping the detectors normal to the solar beam. The tracking head mounts outside the aircraft skin to minimize blockage by aircraft structures and also to avoid data contamination by aircraft-window effects. As noted above, AATS- 14 has been used extensively to test and improve AOD retrievals by MODIS, SeaWiFS, MISR, and many other satellite sensors. Also, AATS-measured AODs have previously been used in atmospheric correction of images of surface scenes.

Headwall Imaging Spectrometer
The Headwall Imaging Spectrometer

Headwall Imaging Spectrometer

The Headwall Imaging Spectrometer is a concentric push-broom hyperspectral imager of the Offner design, which was especially configured by the manufacturer for low-radiance oceanographic remote
sensing. One unique feature of the Offner spectrometer is a curved aberration-corrected diffraction grating that dramatically reduces the spectral distortions (smile and keystone) inherent in standard push-broom systems, which typically use some combination of flat gratings and/or prisms. This system has a very high quality original (as opposed to replicated) holographic grating, which is designed for optimal efficiency at 440 nm, unlike those intended for terrestrial applications. The Offner design allows for a relatively wide field of view without compromising spectral integrity, which is highly desirable for mapping large areas. This system has a 52.5¼ field of view that can be varied with interchangeable objective lenses. With the Offner, all spectra are acquired simultaneously, which is especially critical for an airborne system, where small perturbations of the platform would otherwise result in misregistration of the spectral bands. The system is further customized for ocean imaging with a cooled, blue-enhanced silicon detector array. Manufactured by Q-Imaging Inc., the Retiga-2000RV CCD array has 1600 x 800 elements, and is thermo-electrically cooled to -30¼C for increased sensitivity and radiometric stability. The sealed detector package also reduces the chance of contamination of the array surface due to condensation or dust. The array can be operated with variable regions-of-interest and binning schemes.

Prototype of a set of microradiometers.


The Biospherical Instruments microradiometers design was developed in response to a need for smaller, faster, and potentially less expensive radiometers that could be easily scaled to either more or fewer channels and more easily deployed in coastal waters. The entire assembly, including the photodetector, is located on a single circuit board. Each microradiometer is also equipped with a temperature sensor located close to the photodetector.

Microradiometers are the operational optical sensing units, each with a microprocessor, photodetector, optical filter package, data acquisition system, and communications electronics. Aggregators are used to bundle larger collections of microradiometers and auxiliary sensors (such as temperature) in individual instrument heads. Aggregators control the data flow to and from the microradiometers, they have on-board removable data storage (Micro-SD card) and power control, and have additional sensing roles including tilt angles, input voltage and current, internal humidity and temperature.

The proposed unit includes 19-brass-encased interchangeable individual microradiometers (for different applications) and one aggregator assembly. Included in the band selection are six bands commonly used for ocean color since the onset of the SeaWiFS mission. Also wavelengths are available down to 305 nm, so application-specific sensors such as UV-bands for CDOM or atmospheric correction, bands targeting phycocyanin and phycoerythrin pigments for flights over reservoirs and terrestrial waters (blue-green algae detection), or bands targeting natural fluorescence (for red tide, high sediment load, and primary production applications) could be added. The microradiometer device is sensitive enough to detect moonlight in downward irradiance, yet remain unsaturated when viewing the solar disk in radiance mode

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