On-orbit radiometric and spectral calibration characteristics of EO-1 Hyperion derived with an underflight of AVIRIS and in situ measurements at Salar de Arizaro, Argentina

A calibration experiment was orchestrated on February 7, 2001 at the Salar de Arizaro, Argentina to assess the on-orbit radiometric and spectral calibration of Hyperion. At this high-altitude homogeneous dry salt lakebed, Hyperion, Airborne Visible/Infrared Imaging Spectroradiometer (AVIRIS) and in situ measurements were acquired. At a designated calibration target on Salar de Arizaro, the radiance spectra measured by Hyperion and AVIRIS were compared. In the spectral range from 430-900 nm [visible near-infrared (VNIR)], the ratio of Hyperion over AVIRIS was 0.89, and in the 900 2390-nm [shortwave infrared (SWIR)] spectral range the ratio was 0.79. A comparison of the Hyperion radiance spectrum with a radiative-transfer-code-predicted spectrum for the calibration target showed similar results. These results in conjunction with prelaunch laboratory measurements, on-orbit lunar measurements, other on-orbit calibration experiment results, as well as comparison with Landsat-7, lead to an update of Hyperion radiometric calibration in,December 2001. The compromise update wag to increase the Hyperion radiometric calibration coefficients by 8% in the VNIR and 18% in the SWIR spectrometers. In addition to radiometric accuracy, the on-orbit radiometric precision of Hyperion was assessed at Salar de Arizaro. Noise-equivalent delta radiance was calculated from Hyperion dark signal data and found to be five to ten times higher in comparison to AVIRIS. Also, from a homogeneous portion of Salar de Arizaro the Hyperion SNR was estimated at 140 in the VNIR and 60 in the 2200-nm region of the SWIR spectral range. Cross-track radiometric response was assessed with the AVIRIS dataset that spanned the full Hyperion swath. Within the accuracy of the registration of the datasets, the Hyperion cross-track response was shown to be uniform. Hyperion spectral calibration was assessed with a spectral fitting algorithm using the high spectral resolution radiative transfer modeled spectra for Salar de Arizaro. In the VNIR spectrometer, at the 760-nm oxygen hand, the full cross-track spectral position and full-width at half-maximum (FWHM) of Hyperion were determined. In comparison to the laboratory calibration, spectral shifts ranging from +0.38 to +1.39 nm were derived depending on cross-track spectral position. The on-orbit-derived FWHM ranged from -0.28 to +0.71 nm with respect to the laboratory values. Cross-track spectral calibration was also derived at the 1140-nm water vapor and 2010-nm carbon dioxide absorption features in the SWIR spectrometer.. At 1140 nm, the on-orbit spectral calibration was shifted from +2.2 to +2.5 nm with respect to the laboratory. At 2010 nm, the on-orbit shift was from +3.0 to +3.5 nm compared to the laboratory calibration. These measurements, analyses, and results provide an on-orbit assessment as well as values for update of the Hyperion radiometric and spectral calibration. The calibration experiment at Salar de Arizaro demonstrates a suite of methodologies to assess imaging spectrometer spectral and radiometric characteristics on-orbit. This approach may also be used to monitor these characteristics through time. These Hyperion results further establish the importance of assessment and update of imaging spectrometer measurement characteristics in the operational environment.