Rock-Type Discrimination from Ratioed Infrared Scanner Images of Pisgah Crater, California

Bandpass-resampling effects for the retrieval of surface emissivity

The retrieval of surface emissivity in the 8-14-microm region from remotely sensed thermal imagery requires channel-averaged values of atmospheric transmittance, path radiance, and downwelling sky flux. Band-pass resampling introduces inherent retrieval errors that depend on atmospheric conditions, spectral region, bandwidth, flight altitude, and surface temperature. This simulation study is performed for clear sky conditions and moderate atmospheric water vapor contents. It shows that relative emissivity retrieval errors can reach as much as 3% for broadband sensors (1-2-microm bandwidth) and 0.8% for narrowband instruments (0.15 microm), even for constant surface emissivity. For spectrally varying surface emissivities the relative retrieval error increases for the broadband instrument by approximately 2% in channels with strong emissivity changes of 0.05-0.1. The corresponding retrieval errors for narrowband sensors increase by approximately 3-4%. The channels in the atmospheric window regions with lower transmittance, i.e., 8-8.5 and 12.5-14 microm, are most sensitive to retrieval errors.

N-color (hg,cd)te photodetectors

N-color (Hg,Cd)Te photodetectors capable of spectral band analysis have been fabricated, tested, and delivered. This paper discusses the state of the art in (Hg,Cd)Te n-color photoconductive detectors. Included is a discussion of narrow band two-color devices responsive in the region of 8-14 micro. D*lambda (lambda(p), 10 kHz, 1) higher than 3.5 x 10(9) cm Hz((1/2))/W have been achieved in both top and bottom elements at 95 K. The top element exhibited a cutoff wavelength of 8.8 micro, while the bottom element was responsive from 9.6 micro to 11.1 micro. The device was assembled with a long-wavelength pass filter that yielded two narrow bands. Preliminary results are also included for a unique three-color (Hg,Cd) Te device with cutoff wavelengths of 9.1 micro, 10.8 micro, and 13.8 micro.

Infrared Spectral Emittance in Geological Mapping: Airborne Spectrometer Data from Pisgah Crater, California

Measurements of spectral emittance in the infrared region from 6.8 to 13.3 micrometers were made with an airborne spectrometer at a rate of six spectra per second, on flights 650 meters above the olivine basalt flows at Pisgah Crater in the southern Californian desert. The spectra show chemical and mineralogical differences that can be related to differences in the terrain below the aircraft.