Betina Pavri

Imaging spectroscopy and the airborne visible/infrared imaging spectrometer (AVIRIS)

Abstract Imaging spectroscopy is of growing interest as a new approach to Earth remote sensing. The Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) was the first imaging sensor to measure the solar reflected spectrum from 400 nm to 2500 nm at 10 nm intervals. The calibration accuracy and signal-to-noise of AVIRIS remain unique. The AVIRIS system as well as the science research and applications have evolved significantly in recent years. The initial design and upgraded characteristics of the AVIRIS system are described in terms of the sensor, calibration, data system, and flight operation. This update on the characteristics of AVIRIS provides the context for the science research and applications that use AVIRIS data acquired in the past several years. Recent science research and applications are reviewed spanning investigations of atmospheric correction, ecology and vegetation, geology and soils, inland and coastal waters, the atmosphere, snow and ice hydrology, biomass burning, environmental hazards, satellite simulation and calibration, commercial applications, spectral algorithms, human infrastructure, as well as spectral modeling.

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 was 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.

Steep-sided domes on Venus - Characteristics, geologic setting, and eruption conditions from Magellan data

A survey of more than 95 percent of the Venus surface reveals 145 steep-sided domes which can be subdivided into a variety of morphologic forms, the most common being shaped like inverted bowls or flat-topped domes. Results of a preliminary analysis of the distribution and geologic setting of the domes are presented. The relation of the domes to analogous terrestrial features is examined, and possible models for their mode of emplacement are outlined.

Dawn: An Ion-Propelled Journey to the Beginning of the Solar System

The Dawn mission is designed to perform a scientific investigation of the two most massive main-belt asteroids Vesta and Ceres. These bodies are believed to preserve records of the physical and chemical conditions present during the formation of the solar system. The mission uses an ion propulsion system to enable the single Dawn spacecraft and its complement of scientific instruments to orbit both of these asteroids. Dawns three science instruments - the gamma ray and neutron detector, the visible and infrared mapping spectrometer, and the primary framing camera - were successfully tested after launch and are functioning normally. The ion propulsion system includes three ion thrusters of the type flown previously on the National Aeronautics and Space Administrations (NASAs) Deep Space 1 mission. A minimum of two ion thrusters is necessary to accomplish the Dawn mission. Checkout of two of the ion thrusters was completed as planned within 30 days after launch. This activity confirmed that the spacecraft has two healthy ion thrusters. While further checkout activities are still in progress, the activities completed as of the end of October indicate that the spacecraft is well on its way toward being ready for the start of the thrusting-cruise phase of the mission beginning December 17, 2007.

On-orbit calibration of an ocean color sensor with an underflight of the airborne visible/infrared imaging spectrometer (AVIRIS)

Abstract Accurate calibration of ocean color sensors in the orbital environment is essential to achieve the objectives for which these sensors were proposed, developed, and launched. However, the trauma of launch and the orbital environment may cause changes in sensor calibration. An innovative approach to calibrating ocean color sensors uses the simultaneous underflight of the spaceborne ocean color sensor by a calibrated airborne imaging spectrometer. On May 20, 1997, the high-altitude Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) underflew the Ocean Color and Temperature Scanner (OCTS) onboard the Advanced Earth Observing System (ADEOS) satellite. AVIRIS measures the total upwelling spectral radiance from 400 to 2500 nm at 10-nm intervals at high radiometric and spatial resolution. This spectral range includes the eight ocean bands of OCTS. The spectral, radiometric, and spatial calibrations of AVIRIS are determined in the laboratory and validated in flight. The AVIRIS underflight was designed to match the observation geometry of OCTS. An ocean surface calibration target was determined based on common azimuth and zenith observation. The AVIRIS spectra of the calibration target were corrected to the top of the atmosphere radiance and convolved to the OCTS spectral, radiometric, and spatial characteristics. These AVIRIS data were then used in conjunction with the OCTS data to calculate an on-orbit calibration for OCTS with uncertainty analysis.