On-Orbit Calibration of the EO-1 Hyperion and Advanced Land Imager (ALI) Sensors Using the LED Spectrometer (LSpec) Automated Facility

Vicarious calibration (VC) technology, developed in the mid-1980s, has been employed to establish the absolute radiometric calibration of Earth-viewing sensors aboard satellites and aircraft. This method has heretofore required special visits by a field team to collect surface and atmospheric measurements, at specific times necessarily coincident with a sensor overflight. With the recent creation of an autonomous calibration facility, VC data can now be made available to the sensor community without the need for each research group to deploy its own field team. Beginning in mid-November 2006, there have been ongoing efforts to expand the data processing capabilities of the Jet Propulsion Laboratory-operated LED Spectrometer (LSpec) automatic facility, which has been making continual measurements of surface reflectances and atmospheric transmittances since that time. The facility is located at Frenchman Flat, within the Nevada Test Site. Data are used to support the VC of sensors which make observations at visible and near-infrared wavelengths. An array of eight LSpecs performs the autonomous function of recording surface reflectances at 5-min intervals, thereby permitting accurate and continual real-time adjustments to high-resolution Analytical Spectral Devices spectrometer measurements, acquired every several months during on-site visits. Moreover, resident at the LSpec site is a Cimel sunphotometer, used to make atmospheric transmittance measurements. The Cimel is part of the Aerosol Robotic Network (AERONET). Measurements made by the LSpec Cimel are used by AERONET to derive values of aerosol optical depths. From continuous
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situ
measurement of spectral reflectance of the playa surface, along with acquired aerosol optical depths and ozone optical depths (obtained from the Ozone Mapping Instrument), an LSpec database is being produced and is available via a web-based interface. To highlight the viability of making use of LSpec-derived data, we have executed a few distinct multiple scattering radiative transfer codes in order to perform VCs of the Earth Observing-1 (EO-1) Hyperion and EO-1 Advanced Land Imager sensors.