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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Observations of polar ice using enhanced resolution microwave scatterometer data

Increasing interest in the role of ice sheets in regulating global climate has created a need for synoptic interannual recording and monitoring of the earth's major ice sheets. Based on their ability to 'see' into ice, microwave remote sensing instruments are well-suited for monitoring the polar regions. Although microwave radar has increased capabilities over some aspects of visible wavelength systems, there are tradeoffs between spatial and temporal resolution. Synthetic aperture radar (SAR) can make high resolution images, but is limited in ground coverage over polar regions because of high data rates and a lack of receiving stations. Microwave scatterometers, originally designed for measuring winds over the ocean, are capable of greater ground coverage in polar regions, but are inherently low resolution instruments. However, a recently developed resolution enhancement technique can generate enhanced resolution scatterometer images. In this paper the algorithm is applied to create enhanced resolution images from Seasat and ERS-1 scatterometer data over. Time series of medium-scale radar images for Greenland and Antarctica and the surrounding seas are presented. The growth and shrinkage of the southern polar sea-ice throughout a full annual cycle is illustrated with the seasonal cycle of patterns on the Antarctic and Greenland Ice Sheets clearly evident. Using the time series and simple scattering models, the locations of key ice facies in Greenland are determined.

Long, David G.↗
NASA NTRS1995

Application of Spaceborne Scatterometer to Study Typhoon, Tropical Hydrologic Balance and El Nino

The high spatial resolution and global coverage of a spaceborne microwave scatterometer make it a power instrument to study phenomena ranging from typhoon to El Nino Southern Oscillation which have regional and short term economic and ecological impacts as well as effects on long term and global climate changes. In this report, the application of scatterometer data, by itself, to study the intensity and the evolution of typhoon is demonstrated. The potential of combining wind vector and precipitable water derived from two spaceborne sensors to study the hydrologic balance in the tropics is discussed. The role of westerly wind bursts as a precursor of anomalous warming in the equatorial Pacific is investigated with coincident data from microwave scatterometer, altimeter and radiometer.

Liu, W. Timothy↗
NASA NTRS2000

Hydrological Balance in Tropical Cyclones with Scatterometer and TRMM Data

Precipitation over oceans can be estimated from the radar and the microwave radiometer of the Tropical Rain Measuring Mission (TRMM). It can also be estimated from the divergence of the vertically integrated water vapor transport, through the conservation principle, assuming evaporation is relatively small. In tropical cyclones, the divergence of vertically integrated water vapor is highly dependent on the vertical transport and, therefore, on the wind divergence. Spaceborne scatterometers provide surface wind velocity and, therefore, surface wind divergence at spatial resolutions that are much higher than products of numerical weather prediction (NWP). In this study, ocean surface winds derived from the observations of space-based scatterometers and surface precipitation measured by TRMM were objectively interpolated to the same time and location during the passage of a tropical cyclone. Surface precipitation distribution was derived from wind and humidity profiles provided by NWP. When the surface level winds of NWP were replaced by the scatterometer winds, the surface precipitation patterns computed with the conservation method were found to be significantly changed and the new patterns are much closer in agreement with the patterns observed by TRMM.

Liu, W. Timothy↗
NASA NTRS2000

SeaWinds Scatterometer on QuikSCAT Mission and the Emerging Land and Ocean Applications

Spaceborne scatterometers are active microwave radar instruments designed to acquire near-simultaneous, spatially collocated measurements of the normalized radar backscattering cross section (sigma0) of the global surface from several azimuth and/or incidence angles. The primary objective of the scatterometer mission is to measure the near-surface wind speed and direction over the global ocean using sigma0 measurements together with a wind geophysical model function. However, since sigma0 measurements are collected globally all the time, sigma0 data can also be used for global land and ice applications. In this paper, we will first present the objectives of the QSCAT mission, the instrument design, and the unique features of the Ku-band scatterometer currently in operation, called SeaWinds on QuikSCAT (QSCAT). We will then present some emerging land and ocean applications of the QSCAT data, which include (1) global snow detection and monitoring, (2) melt region mapping on the Greenland ice sheet, (3) Monsoon flood detection and monitoring, (4) soil wetness application at large scale, and (5) hurricane monitoring and tracking.

Tsai, W.-Y.↗
NASA NTRS1999

On-orbit Calibration of the Seawinds Scatterometer Antennas

Measurements of ocean, sea-ice and terrain geophysical parameters can be remotely sensed using an active microwave sensor known as the microwave scatterometer. Satellite scatterometers are spaceborne radars that measure the absolute backscattered power from the earth's surface; and from this measurement, the normalized radar cross-section (sigma(sup 0)) of that surface is determined. Scatterometers calculate sigma(sup 0) of a measurement cell by inverting the radar equation [1]: where: R is range to the cell center, P(sub t) is transmitted power, lambda is transmitted wavelength, L is total path loss, G(sub A) is peak antenna gain, A(sub c) is cell area, and c is a pre-computed factor due to the approximation of the radar equation for extended area targets.

Zec, Josko↗
NASA NTRS1996

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↗
NASA NTRS2016

Understanding Oceanic Heavy Precipitation Using Scatterometer, Satellite Precipitation, and Reanalysis Products

The primary aim of this study is to understand the heavy precipitation events over Oceanic regions using vector wind retrievals from space based scatterometers in combination with precipitation products from satellite and model reanalysis products. Heavy precipitation over oceans is a less understood phenomenon and this study tries to fill in the gaps which may lead us to a better understanding of heavy precipitation over oceans. Various phenomenon may lead to intense precipitation viz. MJO (Madden-Julian Oscillation), Extratropical cyclones, MCSs (Mesoscale Convective Systems), that occur inside or outside the tropics and if we can decipher the physical mechanisms behind occurrence of heavy precipitation, then it may lead us to a better understanding of such events which further may help us in building more robust weather and climate models. During a heavy precipitation event, scatterometer wind observations may lead us to understand the governing dynamics behind that event near the surface. We hypothesize that scatterometer winds can observe significant changes in the near-surface circulation and that there are global relationships among these quantities. To the degree to which this hypothesis fails, we will learn about the regional behavior of heavy precipitation-producing systems over the ocean. We use a "precipitation feature" (PF) approach to enable statistical analysis of a large database of raining features.

Winds↗
NASA NTRS1996

Sea Ice Identification using Dual-Polarized Ku-Band Scatterometer Data

This paper describes a classification algorithm using dual-polarized scatterometer measurements to identify the edge of the sea ice cover. The distinct polarization scattering of sea ice and open water are discussed and illustrated with the dual-polarized radar measurements from the Seasat-A scatterometer (SASS).

Sea↗
NASA NTRS1997

Application of Cylindrical Near-Field Measurement Technique to The Calibration of Spaceborne Radar Antennas: NASA Scatterometer and SeaWinds

Modern spaceborne radar scatterometers such as the NASA Scatterometer (NSCAT) and SeaWinds radar instruments require precise determination of the normalized backscattered radar cross section within a few tenth of a decibel in order to achieve the desired wind velocity and direction measurement accuracy of 2 m/s and 20 degrees respectively.

Spaceborne Radar Antennas SeaWinds Scatterometer↗
NASA NTRS1994

The SeaWinds Scatterometer Instrument

The SeaWinds scatterometer instrument is currently being developed by NASA/JPL, as part of the NASA EOS Program, for flight on the Hapanese ADEOS II mission in 1999. This Ku-band radar scatterometer will infer surface wind speed and direction by measuring the radar normalized backscatter cross-section over several different azimuth angles. This paper presents the design characteristics of and operational approach to the instrument itself.

SeaWinds scatterometer EOS program ADEOS II Ku-ban↗
NASA NTRS2006

The Aquarius Scatterometer: An Active System for Measuring Surface Roughness for Sea-Surface Brightness Temperature Correction

The Aquarius scatterometer is a total-power L-band radar system for estimating ocean surface roughness. Its measurements will enable the removal of wind effects from the Aquarius radiometer ocean-surface brightness temperature measurements being used to retrieve ocean salinity. The Aquarius scatterometer is a relatively simple, low-spatial resolution power-detecting radar, without ranging capability. But to meet its science requirement, it must be very stable, with repeatability on the order of 0.1 dB over several days, and calibrated accuracy to this level over several months. Data from this instrument over land as well as ocean areas will be available for a variety of geophysical applications.

scatterometers↗
NASA NTRS2000

Azimuth variation in microwave scatterometer and radiometer data over Antarctica

In this paper, we explore the use of NASA scatterometer (NSCAT) data, European remote sensing (ERS) advanced microwave instrument (AMI) scatterometer mode data, and special sensor microwave/imager (SSM/I) data to study surface roughness effects in Antarctica. All three sensors provide strong evidence of azimuth modulation, which is correlated with the surface slope environment and results in a katabatic wind flow regime.

azimuthal↗
NASA NTRS1972

Detection of oil spills using 13.3 GHz radar scatterometer

The results of an analysis of 13.3-GHz single polarized scatterometer data collected during NASA/MSC Mission 135, flown on March 16, 1970 are reported. Data were gathered over a crude oil spill on the Gulf of Mexico off the Mississippi Delta. With the aid of RC-8 camera photographs, the scattering cross section was correlated with the extent of the oil spill. The scattering cross section at higher incidence angles decreased by 5 db to 10 db in the presence of the oil spill. This was attributed to oil's damping of small gravity and capillary waves. The composite scattering theory and the scatterometer acquired data were used to obtain an expression of radar scattering over ocean surfaces with oil spills. The study demonstrates that the presence and extent of oil spills can be detected using high frequency radar systems.

Krishen, K.↗
NASA NTRS1973

Detection of oil spills using a 13.3-GHz radar scatterometer.

This paper describes the results of an analysis of 13.3-GHz single-polarized scatterometer data collected during NASA/MSC mission 135, flown on March 16, 1970. Data were gathered over a crude oil spill on the Gulf of Mexico (test site 128) off the Mississippi delta. With the aid of RC-8 camera photographs the scattering cross section was correlated with the extent of the oil spill. The scattering cross section at higher incidence angles (25 to 50 deg) decreased by 5-10 db in the presence of the oil spill. This was attributed to the damping by oil of small gravity and capillary waves. The composite scattering theory and the scatterometer-acquired data were used to obtain an expression of radar scattering over ocean surfaces with oil spills. The study demonstrates that the presence and extent of oil spills can be detected with high-frequency radar systems.

Krishen, K.↗
NASA NTRS1973

Agricultural terrain scatterometer observations with emphasis on soil moisture variations

Airborne scatterometer observations were made for agricultural terrain in May and June, 1970 at a NASA test site near Garden City, Kansas. Data from 13.3 GHz and 400 MHz scatterometer were analyzed. It was observed that for incidence angle less than 40 degrees, the 13.3 GHz data showed a difference in backscatter from wet and dry fields of the order of 7 db. The averages of the various crop types were within a spread of only 5 db. Other ground parameters such as cultivation pattern and vegetation row effects showed even less distinguishing characteristics on the backscatter. The 400 MHz data also showed a slight moisture dependency.

King, C.↗