Phillip W. Dabney

Design and performance of a 3D imaging photon-counting microlaser altimeter operating from aircraft cruise altitudes under day or night conditions

The present paper reports on the design and performance of a scanning, photon-counting laser altimeter, capable of daylight operations from aircraft cruise altitudes. In test flights, the system has successfully recorded high repetition rate returns from clouds, soils, man-made objects, vegetation, and water surfaces under full solar illumination. Following the flights, the signal was reliably extracted from the solar noise background using a Post- Detection Poisson Filtering technique. The passively Q-switched microchip Nd:YAG laser measures only 2.25 mm in length and is pumped by a single 1.2 Watt GaAs laser diode. The output is frequency-doubled to take advantage of higher detector counting efficiencies and narrower spectral filters available at 532 nm. The transmitter produces several microjoules of green energy in a subnanosecond pulse at rates approaching 10 kHz. The illuminated ground area is imaged by a 14-cm diameter, diffraction-limited, off-axis telescope onto a segmented anode photomultiplier. Each anode segment is input to one channel of fine range receiver (5-cm resolution), which records the times-of-flight of individual photons. A parallel coarse receiver provides a lower resolution (greater than 75 cm) histogram of all scatterers between the aircraft and ground and centers the fine receiver gate on the last set of returns.

Advanced Solid-State Array Spectroradiometer support of 1989 field experiments

An overview of the ASAS data acquired in support of the 1989 field experiments is presented and data quality is discussed. The precision of the ASAS data is considered through the presentation of SNRs derived from both field and laboratory data. ASAS is an airborne, off-nadir pointing, imaging spectroradiometer that acquires digital image data for 29 visible and near-infrared spectral bands (465 to 871 nm) with a spectral resolution of 15 nm. Surfaces observed for the field experiments include volcanic surfaces and a playa within a sparsely vegetated semiarid ecosystem, grass canopies within a prairie ecosystem, and tree canopies within a northern forest ecosystem. It is shown that calibrated ASAS data are sufficiently exact for investigations of the directional distribution of radiation scattered from terrestrial surfaces.

The 2011 Eco3D flight campaign: Vegetation structure and biomass estimation from simultaneous SAR, lidar and radiometer measurements

The Eco3D campaign was conducted in the Summer of 2011. As part of the campaign three unique and innovative NASA Goddard Space Flight Center airborne sensors were flown simultaneously: The Digital Beamforming Synthetic Aperture Radar (DBSAR), the Slope Imaging Multi-polarization Photon-counting Lidar (SIMPL) and the Cloud Absorption Radiometer (CAR). The campaign covered sites from Quebec to Southern Florida and thereby acquired data over forests ranging from Boreal to tropical wetlands. This paper describes the instruments and sites covered and presents the first images resulting from the campaign.

Pushbroom Laser Altimetry using Fiber Lasers and Photon Counting Detectors

We report on progress in developing a new swath mapping laser altimeter measurement approach using multiple laser measurement beams, modulated fiber lasers, photon counting detectors, and event timers for future space missions.

BOREAS RSS-2 Extracted Reflectance Factors Derived from ASAS Imagery

The BOREAS RSS-2 team derived atmospherically corrected bidirectional reflectance factor means from multispectral, multiangle ASAS imagery for small homogeneous areas near several BOREAS sites. The ASAS imagery was acquired from the C-130 aircraft platform in 1994 and 1996. The data are stored in tabular ASCII files.

Estimating Hemispherical Reflectance and Selected Biophysical Parameters for Boreal Forest Canopies

Advanced Solidstate Array Spectroradiometer (ASAS) hyperspectral, multiangle data were obtained over BOREAS sites in Saskatchewan and Manitoba, Canada during four field campaigns in 1994. Flown aboard the NASA C130B at an altitude of approximately 5000 m above ground level, ASAS acquired off-nadir data from 70 degrees forward to 55 degrees aft along-track, in 62 contiguous spectral bands ranging from 400-1025 nm. These measurements were collected to develop linkages between optical remote sensing data and biophysical parameters at the canopy level, and to provide an intermediate level in the process of scaling local ground conditions to satellite observations. ASAS at-sensor radiances over various canopies were atmospherically corrected using the Second Simulation of the Satellite Signal in the Solar Spectrum (6s) and at-surface reflectance factors were derived. Using the multiangle spectral reflectance factors, spectral hemispherical reflectance (PAR, red, and nir) was estimated, and spectral vegetation indices, including hemispherical measures, were calculated. The values of the SVIs varied widely depending on the particular angular inputs to the calculation.

Estimating hemispherical reflectance and selected biophysical parameters for boreal forest canopies using spectral bidirectional reflectance data acquired by ASAS

Advanced Solidstate Array Spectroradiometer (ASAS) hyperspectral, multiangle data were obtained over BOREAS sites in Saskatchewan and Manitoba, Canada during four field campaigns in 1994. Flown aboard the NASA C-130B at an altitude of approximately 5000 m above ground level, ASAS acquired off-nadir data from 70 degrees forward to 55 degrees aft along-track, in 62 contiguous spectral bands ranging from 400-1025 nm. These measurements were collected to develop linkages between optical remote sensing data and biophysical parameters at the canopy level, and to provide an intermediate level in the process of scaling local ground conditions to satellite observations. ASAS at-sensor radiances over various canopies were atmospherically corrected using the Second Simulation of the Satellite Signal in the Solar Spectrum (6S) and at-surface reflectance factors were derived. Using the multiangle spectral reflectance factors, spectral hemispherical reflectance (PAR, red, and near-IR) was estimated, and spectral vegetation indices, including hemispherical measures, were calculated. The values of the SVIs varied widely depending on the particular angular inputs to the calculation.

Calibration and characterization of an airborne pushbroom spectroradiometer

Improved methods for calibrating and characterizing the CCD array based off-nadir tiltable advanced solid-state array spectroradiometer (ASAS) were developed and applied. Sensor characteristics such as radiometric sensitivity, polarization sensitivity, signal-to-noise-ratio, temperature sensitivity, spectral bandpass, spectral distortion, spatial distortion, and spatial resolution were measured. Radiometric sensitivity, array temperature sensitivity, and signal-to-noise were measured using a barium sulfate coated integrating hemisphere whose output calibration is traceable to NIST. Polarization sensitivity was measured for 48 of 62 spectral bands across all 512 spatial pixels. Spectral bandpass and spectral distortion were measured using a 0.5 meter doublepass monochromator. Spatial resolution (given as the modulation-transfer-function -- MTF) and distortion were measured using a combination of monochromatic collimated light to directly measure the point-spread-function (PSF) and the edge spread function (ESF) derived from actual image data. The MTF obtained using the two techniques are compared. Potential improvements to the test setups and methods are described.

Calibration methods and results for the Advanced Solid-State Array Spectroradiometer (ASAS)

Improved methods for calibrating and characterizing the CCD array based off-nadir tiltable advanced solid-state array spectroradiometer (ASAS) were developed and applied. Sensor characteristics such as radiometric sensitivity, polarization sensitivity, signal-to-noise ratio, temperature sensitivity, spectral bandpass, spectral distortion, and spatial resolution were measured. Radiometric sensitivity, array temperature sensitivity, and signal-to-noise were measured using a barium sulfate coated integrating hemisphere whose output calibration is traceable to NIST. Polarization sensitivity was measured for 62 spectral bands across all 512 spatial pixels (31 K pixels). Spectral bandpass and spectral distortion were measured using a 0.5 meter doublepass monochromator. Spatial resolution (given as the modulation-transfer-function -- MTF) and distortion were measured using a combination of monochromatic collimated light to directly measure the point-spread-function (PSF) and the edge spread function (ESF) derived from actual image data. The MTF obtain using the two techniques are compared. Potential improvements to the test setups and methods are described.