James E. Kalshoven

Remote sensing of the Earth's surface with an airborne polarized laser

A new remote sensing instrument, the Airborne Laser Polarization Sensor (ALPS), is making the first multispectral radiometric and polarization measurements of the Earths surface using a polarized laser light source. Results from data flights taken over boreal forests in Maine at 1060 and 532 nm, using a Nd:YAG laser source, showing depolarization signatures for three broadleaf and five coniferous tree species, are discussed. Measurements made over nonforest ground cover had a large dynamic range in depolarization values at both wavelengths. The ALPS system use twelve photomultiplier tube detectors configurable to measure desired parameters such as the total backscatter and the polarization state, including the azimuthal angle and ellipticity, at different ultraviolet to near-infrared wavelengths simultaneously. Measurements of the azimuth and ellipticity of the backscatter polarization were variable and no specific conclusions have yet been drawn. >

Laser remote sensing of atmospheric temperature by observing resonant absorption of oxygen

Measurement of atmospheric temperature through the monitoring of laser energy absorption at the center of an O(2) resonant absorption line near 770 nm has been demonstrated using a dual frequency system. The average temperature of a 1-km path can be determined to better than 1.0 degrees C with a noise level of 0.3 degrees C. An iterative algebraic expression for determining temperature from the measured absorption was developed and shown to be applicable in the troposphere. The effects of pressure and humidity on temperature determination are clear from the algorithm and found to be small near the earths surface.

Remote sensing of crop parameters with a polarized, frequency-doubled Nd:YAG laser

Polarized laser remote-sensing measurements that correlate the yield, the normalized difference vegetation index, and the leaf area index with the depolarized backscattered radiation from corn plots grown with eight different nitrogen fertilization dosages are presented. A polarized Nd:YAG laser emitting at 1064 and 532 nm is used. Depolarization increased significantly with increasing fertilization at the infrared wavelength, and there was a decrease in the depolarization at the green wavelength. The depolarization spectral difference index, defined as the absolute difference in the depolarization at the two wavelengths, is introduced as a parameter that is an indicator of the condition of the internal leaf structure.

Multicolor laser altimeter for barometric measurements over the ocean - Experimental

Measurement theory and results from testing a breadboard multiwavelength (355-, 532- and 1064-nm) laser altimeter over horizontal paths are presented. They show that pressure accuracies of 3 mbar can be achieved when ranging at nadir to cube corner targets when using a 500-psec resolution waveform digitizer and utilizing new calibration techniques. Streak camera-based receivers will be required for the same or higher accuracies when ranging to the ocean surface. System design calculations for aircraft and spaceborne experiments are presented.

Measurements of Stokes parameters of materials at 1064-nm and 532-nm wavelengths

Laser radar systems have found wide applications in the field of remote sensing. Reflectance as well as polarization features are used together for applications ranging from environmental monitoring to target classification. The Stokes parameters are ideal quantities for characterizing the above features because they provide useful information on both light intensity and polarization state. The University of Nebraska is currently refurbishing an airborne multi-wavelength laser radar system based on the NASA Goddard Space Flight Center (GSFC) developed Airborne Laser Polarimetric Sensor (ALPS). The system uses a Nd:YAG laser operating at wavelengths of 1064 nm and 532 nm, and contains four channels at each wavelength to measure the polarization states. This system was used to measure the Stokes parameters of backscattered laser light from different materials. These included canvas tarp, white paper, plywood, concrete, aluminum plate and anodized aluminum plate. The data provide an understanding of the polarized scattering properties of various materials, and are expected to be useful in developing target discrimination algorithms.

Airborne ground illuminator for hyperspectral validation and calibration

A major difficulty in accurately quantifying various of the Earths geophysical and biophysical features from the multi- spectral reflectance data acquired from space is the lack of extensive and reliable validation measurements from good ground truth. A new, active airborne sensor system, AVIS (airborne vegetation index sensor), addresses that problem. AVIS uses a flash lamp mounted on a NASA helicopter to illuminate the Earth with a 15 by 35 mrad spot. The visible and near-IR backscattered radiation is then received hyperspectrally and can be analyzed. Initially designed for validation of theories on vegetation index determination, AVIS has broad application as a simulator for solar illumination for remote surface analysis. Its primary advantage is the reduction or elimination of atmospheric scattering and solar angle effects, and the removal of shadowing. It also provides repeatability for time analysis over the same sites.

Tapping into a Billion Dollar Resource, SBIR/STTR

This presentation provides an overview of the Small Business Innovation Research (SBIR) and the Small Business Technology Transfer (STTR) Programs as implemented by the National Aeronautics and Space Administration (NASA). These programs, as mandated by Congress, provide an opportunity for small, high technology companies and research institutions to participate in Government sponsored research and development (R&D) efforts in key technology areas. This presentation describes the background and operation of these two programs and discusses what factors a business should consider in making the decision to participate.

Performance criteria for remote sensing with spaceborne linear array detectors

A NASA laboratory for evaluating linear detector arrays for remote sensing applications from the visible to shortwave infrared is described. Nominal requirements for acceptable sensor performance are presented for the critical parameters of signal-to-noise ratio, modulation transfer function, response linearity, dynamic range, and detector-to-detector response uniformity. Results of tests are presented for a custom-developed multispectral linear array from RCA and two commercial arrays from Texas Instruments and Reticon for the visible and near infrared. The custom array was clearly superior to its off-the-shelf counterparts in signal-to-noise ratio and dynamic range. All the arrays were found to have somewhat less than desirable modulation transfer functions but excellent response linearity.

Two Complimentary Methods For Aligning Linear Arrays

Two complimentary methods for aligning a linear array of detectors are described. The alignment procedure effectively projects a set of reference coordinators as defined by the intersection of a laser beam with the interface of a pair of matched cube beamsplitters. The fractional (radiometric) error associated with this alignment procedure should be much less than 0.1%.

Evaluation of multi-spectral linear array detectors for spaceborne applications

A NASA laboratory for evaluating linear detector arrays for remote sensing applications from the visible to shortwave infrared is de-scribed. Nominal requirements are presented on the critical parameters of signal-to-noise ratio, modulation transfer function, response linearity, dynamic range, and detector-to-detector response uniformity. Results of tests on a custom developed multi-spectral linear array from RCA and two commercial arrays from Texas Instruments and Reticon for the visible and near-infrared are presented. The custom array was clearly superior in signal-to-noise ratio and dynamic range to its off-the-shelf counterparts. All the arrays were found to have somewhat less than desirable modulation transfer functions, but excellent response linearity.