Scatterometer image data for global ice and land climate studies
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polar oceanography land studies scatterometer↗
Engineering topics
Long, D. G.
Publications and source records attributed to Long, D. G..
An iterative approach to multisensor sea ice classification
Characterizing the variability in sea ice in the polar regions is fundamental to an understanding of global climate and the geophysical processes governing climate changes.
Aperature↗
Improved Resolution Backscatter Measurements with the SeaWinds Pencil-Beam Scatterometer
The SeaWinds scatterometer will fly on the NASA Quickscat spacecraft in 1998, and on the Japanese ADEOS-II mission in 2000. In addition to providing ocean surface wind estimates for use by weather forcasters, these flights will generate a global Ku-Band backscatter data set for a variety of climate studies.
pencil-beam↗
High Resolution Surface Backscatter Measurements with the SeaWinds Scatterometer
A technique employed to extract higher resolution backscatter measurements from the SeaWinds pencil-beam scatterometer system is described. The unique methodology necessary to achieve very high radiometric accuracy for such measurements is discussed.
backscatter SeaWinds scatterometer radiometry↗
Decadal Changes on the Greenland Ice Sheet Observed by Microwave Radar
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microwave spaceborne scatterometers↗
Imagin Ice Sheet Change Using Scatterometers
Though designed to measure vector ocean winds, new imaging techniques facilitate the use of spaceborne scatterometer data in climate change studies of polar ice sheets.
NASA Ku-band Scatterometer (NSCAT)↗
Tradeoffs in the Design of a Spaceborne Scanning Pencil Beam Scatterometer: Application to Sea Winds
SeaWinds is a spaceborne scatterometer to be flown on the second Japanese Advanced Earth Observation Satellite (ADEOS-II) in 1999. An important international element of NASA's Earth Observing System (EOS), SeaWinds is an advanced follow-on to the NASA scatterometer (NSCAT) on the first ADEOS platform. Unlike previous operational spaceborne scatterometer systems, SeaWinds employs a scanning pencil-beam antenna rather than a fan-beam antenna, making the instrument more compact and yielding greater ocean coverage.
Sea Winds Earth Observing System EOS Advanced Eart↗
Greenland observed at high resolution by the Seasat scatterometer
A previously developed method for the reconstruction of surface radar backscatter characteristics is applied to Seasat scatterometer (SASS) data for the study of Greenland's ice sheet. A time series of the radar backscatter images provides an island-wide view of the ice sheet which shows the extent of the summer melt. Medium-scale scatterometer images provide frequent island-wide observations permitting precise measurements of the seasonal extent of the summer melt.
Long, D. G.↗
High-resolution land/ice imaging using Seasat scatterometer measurements
A new method for obtaining high-resolution images (to 4 km) of the land backscatter from low-resolution Seasat-A scatterometer (SASS) measurements is introduced. The method utilizes the measurement cell overlap in multiple spacecraft passes over the region of interest and signal processing techniques to generate high-resolution images of the radar backscatter. The overlap is exploited to estimate the underlying high-resolution surface radar backscatter characteristics using a robust multivariate image reconstruction algorithm. The algorithm has been designed to operate in the high-noise environment typical of scatterometer measurements. The ultimate resolution obtainable is a function of the number of measurements and the measurement overlap. Sample results based on SASS data are provided.
Long, D. G.↗
The wavenumber spectra of scatterometer-derived winds
The accuracy of scatterometer-derived winds using a frequency-domain analysis and simulation is studied. The wavenumber spectra of the Seasat-A-scatterometer (SASS)-derived wind fields have been observed to be accentuated relative to the input wind field. The results of extensive simulations designed to test this observation are reported. Actual SASS measurements of the normalized radar backscatter (NRB) over an orbit (rev) are used as a template to generate simulated NRB measurements. Pointwise estimation of winds from the simulated NRB measurements is accomplished with the ambiguity closest to the true wind selected as the unique wind vector estimate. For comparison, winds are also estimated using a new model-based approach. After wind retrieval, the spectra of the estimated wind fields are computed and compared to the input wind field. The high wavenumber portion of the spectra of the pointwise estimated winds was higher than the spectra of the true winds by an amount which depends on the wind speed variance.
Long, D. G.↗
Spaceborne radar measurement of wind velocity over the ocean - An overview of the NSCAT scatterometer system
Scatterometry and scatterometer design issues are reviewed. The design of the NASA Scatterometer (NSCAT) to be flown on the Japanese ADEOS mission is presented. Building on Seasat experience, the NSCAT system includes several enhancements, such as three antenna azimuths in each of two swaths, and an onboard digital Doppler processor to allow backscatter measurements to be colocated everywhere within the orbit. These enhancements will greatly increase the quality of the NSCAT wind data. The ground processing of data is discussed, and scatterometers of the next decade are briefly described.
Naderi, F. M.↗
Radar backscatter measurement accuracies using digital Doppler processors in spaceborne scatterometers
The normalized standard deviation, Kp, of radar backscatter measurements using digital Doppler processors in spaceborne scatterometers is derived. The Kp expression for analog Doppler filter processors, such as that used in the Seasat scatterometer is shown to be a special case of the derived Kp expression. A connection to Welch's (1967) power spectrum estimation rsults is also made. Tradeoff studies in digital filter design such as hardware complexity, computational speed, and system performance can be performed based on this Kp expression. A current application in the design of the NASA scatterometer to be flown in 1990 is discussed. This derivation should be useful for system design and analysis of other radar remote-sensing instruments.
Chi, C.-Y.↗