Philip D. Hammer and David L. Peterson (code SGE)

William H. Smith¹

Scientific observations that provide simultaneous spatial (images) and spectral (wavelength dependence) information are a powerful means for studying Earth's environment. Remote sensing of the Earth's radiative fields at visible and infrared wavelengths is an important way of exploring the structure and processes of the surface and atmosphere. Understanding complex and variable environmental phenomena such as light interaction within plant canopies or through clouds in the atmosphere requires spatial, spectral, and temporal observations that are both extensive and detailed. Thus there is considerable motivation for designing simple, versatile and cost effective imaging spectrometers for Earth remote sensing applications.

We have been developing a new technique to make remote measurements that are important for surface and atmospheric sciences. The instrumental concept is called Digital Array Scanned Interferometry (DASI). Recent advances in imaging device technology has made it possible to use this new approach for a variety of scientific studies. DASI instruments have advantages over grating or prism based instruments particularly in regards to compactness, device simplicity, and performance. DASIs have many of the positive characteristics associated with Fourier transform spectrometers (which have been used for several decades for making non-imaging spectral observations) with the additional capability of spatial imaging.

This year, we have published an analysis of cloud measurements made from the ground using DASI. These measured results were compared with model results to obtain information about the properties of the clouds. Additionally, we have made first time airborne observations of the surface using a downward viewing DASI on the NASA C-130 aircraft. The figure shows a selected spectral image derived from these measurements.

¹ Washington University

Ames-Moffett contact: Dr. Philip D. Hammer

hammer@rad.arc.nasa.gov

or tel: (415) 604-3383

Headquarters program office:

Figure 1. Selected result from DASI / C-130 measurement made March 1994. This Aircraft-based observation made over San Joaquin Valley using a DASI equipped with an short wavelength infrared detector array. The image is shown at 5 selected wavenumber values. The diagonal strips at the top is part of a runway. A variety of agricultural fields comprise most of the other features. Spatial resolution was 31 meters long-track (vertical axis) and 2.4 meters cross track. The scene dimensions are 3.1 kilometers long-track and 0.61 kilometers cross track. Spectral resolution was 266 inverse- centimeters corresponding to 17 effective bands within the spectral range of sensitivity.