Engineering topics

Nolin, Anne W.

Publications and source records attributed to Nolin, Anne W..

5 records

NASA NTRS2010

Ten Years of MISR Observations from Terra: Looking Back, Ahead, and in Between

The Multi-angle Imaging SpectroRadiometer (MISR) instrument has been collecting global Earth data from NASA's Terra satellite since February 2000. With its nine along-track view angles, four visible/near-infrared spectral bands, intrinsic spatial resolution of 275 m, and stable radiometric and geometric calibration, no instrument that combines MISR's attributes has previously flown in space. The more than 10-year (and counting) MISR data record provides unprecedented opportunities for characterizing long-term trends in aerosol, cloud, and surface properties, and includes 3-D textural information conventionally thought to be accessible only to active sensors.

remote sensing↗

NASA NTRS2004

Investigating Downscaling Methods and Evaluating Climate Models for Use in Estimating Regional Water Resources in Mountainous Regions under Changing Climatic Conditions

The purpose of this three-year study is to develop and evaluate techniques to estimate the range of potential hydrological impacts of climate change in mountainous areas. Three main objectives are set out in the proposal. (1) To develop and evaluate transfer functions to link tropospheric circulation to regional snowfall. (2) To evaluate a suite of General Circulation Models (GCMs) for use in estimating synoptic scale circulation and the resultant regional snowfall. And (3) to estimate the range of potential hydrological impacts of changing climate in the two case study areas: the Upper Colorado River basin, and the Catskill Mountains of southeastern New York State. Both regions provide water to large populations.

Frei, Allan↗

NASA NTRS1993

Estimating snow grain size using AVIRIS data

Estimates of snow grain size for the near-surface snow layer were calculated for the Tioga Pass region and Mammoth Mountain in the Sierra Nevada, California, using an inversion technique and data collected by the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS). The Tioga Pass and Mammoth Mountain single-band AVIRIS radiance images were atmospherically corrected to obtain surface reflectance. A discrete-ordinate model was used to calculate directional reflectance as a function of snowpack grain size for a wide range of snow grain radii. The resulting radius vs. reflectance curves were each fit using a nonlinear least squares technique which provided a means of transforming surface reflectance in each AVIRIS image to optically equivalent grain size on a per-pixel basis. The model results and grain size estimates derived from the AVIRIS data show that, for solar incidence angles between 0 and 30, the technique provides good estimates of grain size. This work provides the first quantitative estimates for grain size using data acquired from an airborne remote sensing instrument and is an important step in improving our ability to retrieve snow physical properties independent of field measurements.

Nolin, Anne W.↗

NASA NTRS1991

Spectral reflectance of thin snow

A radiative transfer model was used to calculate the spectral reflectance of thin snow overlying dark soil. Model results show that directional hemispherical reflectance depends on density, grain size, and solar and viewing geometries. Measurements of thin snow spectral Bidirectional Reflectance Distribution Function (BRDF) show that the reflectance in the visible wavelengths is reduced when the sensor is near nadir yet, at a viewing zenith of 75 degrees the same snowpack will appear to be optically thick. If the snow is sufficiently thin and snow grains are large, the spectral signature of the substrate may influence snow reflectance. This phenomenon was also detected in reflectance data collected using the ground based PIDAS (Portable Instantaneous Display and Analysis Spectrometer). Concurrent airborne data from the AVIRIS instrument (Advanced Visible/Infrared Imaging Spectrometer) show effects of thin snow and mixed pixels for areas of thin and patchy spring snow.

Nolin, Anne W.↗

NASA NTRS1989

Reflectance and transmittance of snow at high spectral resolution

A radiative-transfer model for the bidirectional reflectance-distribution function (BRDF) shows that snow is moderately anisotropic in the NIR wavelengths. Although the directional-hemispherical albedo of snow decreases as the grains become larger, the forward scattering also increases, with the result that the illumination and viewing geometry must be considered when interpreting physical properties of the surface layer of the snow pack from remote sensing data. Measurements of the BRDF and the transmittance for a variety of snow conditions were made throughout the winter and spring seasons with an SE-590 spectroradiometer, for wavelengths from 0.38 to 1.11 microns. Coincident with these, the surface grain properties were analyzed by stereological methods. A sphere with the same surface-to-volume ratio as the ice grains is used as the equivalent sphere.

Dozier, Jeff↗