James E. Conel

Estimation of aerosol optical depth, pressure elevation, water vapor, and calculation of apparent surface reflectance from radiance measured by the airborne visible/infrared imaging spectrometer (AVIRIS) using a radiative transfer code

The Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) is an imaging spectrometer that measures spatial images of the total up welling spectral radiance from 400 to 2500 nm at 10 nm spectral intervals. Quantitative research and application objectives for surface investigations require conversion of the measured radiance to surface reflectance or surface leaving radiance. To calculate apparent surface reflectance an estimation of aerosol optical depth is required for compensation of aerosol scattering and absorption across the spectral range. Determination of other atmospheric characteristics such as atmospheric water vapor and surface pressure is also required. In this paper we describe a set of algorithms to estimate aerosol optical depth, atmospheric water vapor, and surface pressure height from the AVIRIS measured radiance. Based upon these determined atmospheric parameters we described an algorithm to calculated apparent surface reflectance from the AVIRIS measured radiance using a radiative transfer code.

In-situ atmospheric water-vapor retrieval in support of AVIRIS validation

A comparison is made between two ground-based atmospheric water-vapor measurement techniques, each of which uses data from a solar-pointing radiometer. One technique uses visible wavelength channels to retrieve aerosol loading, surface pressure readings for Rayleigh scattering analyses, and the 0.94 micron channel to extract water vapor from the residual of total versus scattering opacity. The other technique requires only the ratio of channels centered at 0.94 and 0.87 micron. Results are given for the April 13, 1989 AVIRIS in-flight calibration.

In-flight validation and calibration of the spectral and radiometric characteristics of the Airborne Visible/Infrared Imaging Spectrometer

Through an in-flight calibration experiment at Rogers Dry Lake, California on September 20, 1989, the radiometric and spectral properties of AVIRIS were determined. In-flight spectral channel positions and the spectral response function in 10 regions of the AVIRIS spectral range, taking in all four spectrometers, are shown to agree closely with the corresponding parameters measured in the laboratory. The intraflight stability for the Rogers Dry Lake calibration site is better than 2 percent with the exception of the strong atmospheric water absorptions where the measured radiance is close to zero. This experiment has provided both direct generation of an in-flight spectral and radiometric calibration and validation of the laboratory calibration at the reported level accuracy.

Luminescence and reflectance of tranquillity samples: effects of irradiation and vitrification.

Luminescence measurements of Tranquillity samples indicate that energy efficiencies for excitation by protons and ultraviolet are in the range 10-6 or below; natural and induced thermoluminescence is even weaker. If these samples are typical, lunar surface luminescence cannot occur at reported levels. Comparison of proton luminescence spectra from the exterior and interior of rocks and fine fragments provides evidence of solar wind impingement on the moons surface. Spectral reflectance and albedo measurements of fresh rock powders before and after both laboratory proton irradiation and fusion indicate that vitrification may be an important mechanism of lunar darkening.

Inflight validation of the calibration of the Airborne Visible/Infrared Imaging Spectrometer in 1993

To achieve the research objectives of the Airborne Visible/IR Imaging Spectrometer (AVIRIS), the sensor calibration must be valid while AVIRIS is acquiring data from the airborne platform. The operational environment inside the aircraft differs significantly from that in the AVIRIS laboratory environment where the sensor is calibrated prior to and following each flight season. To independently validate the calibration of AVIRIS in the flight environment an inflight calibration experiment is conducted at least twice each flight season. Results for a calibration experiment held on the 26th of September 1993 are presented.

Calibration of the Japanese Earth Resources Satellite-1 optical sensor using the Airborne Visible/Infrared Imaging Spectrometer

In this paper, we describe an experiment to calibrate the Optical Sensor on board the Japanese Earth Resources Satellite-1 with data acquired by the Airborne Visible/IR Imaging Spectrometer. 27 August 1992 both OPS and AVIRIS acquired data concurrently over a calibration target on the surface of Rogers Dry Lake, Nevada. The high spectral resolution measurements of AVIRIS were convolved to the spectral response curves of the OPS. These data, in conjunction with the corresponding OPS digitized numbers, were used to generate the radiometric calibration coefficients for the eight OPS bands. This experiment establishes the suitability of AVIRIS for the calibration of space-borne sensors in the 400-2500 nm spectral region.