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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 NTRS1975

A comparison of Skylab S-193 and aircraft views of surface roughness and a look toward SEASAT

An extensive aircraft underflight program was conducted along the Skylab groundpath for the purpose of documenting wind, wave, and atmospheric conditions affecting the amplitude of the active and passive microwave signatures. The S-193 microwave system senses a roughness parameter at the ocean surface that is proportional to the surface windspeed. The aircraft program is described, and some comparisons of satellite and aircraft results are presented. The principal result of the comparison of active radar is that direct inferences of the surface windspeed are possible, but subject to considerable scatter, and that this scatter appears to be due to interaction between long gravity and short Bragg waves and backscatter due to rain as well as errors in correcting for azimuth dependence. An unforeseen opportunity to observe a Pacific hurricane by both Skylab and NOAA aircraft has contributed to the development of a simplified wave forecasting scheme applicable to hurricanes, and more general conditions, which combines the better qualities of both spectral and height/period forecasting techniques. Horizontal polarization data obtained by the aircraft in Hurricane Ava, and in other experiments, which led to this development are presented.

Ross, D.↗
NASA NTRS1977

Microwave remote sensing of hydrologic parameters

A perspective on the implementation of microwave sensors in future airborne and spaceborne observations of hydrologic parameters is presented. The rationale is based on a review of the status and future trends of active (radar) and passive (radiometer) microwave research as applied to the remote sensing of soil moisture content, snowpack water equivalent, freeze/thaw boundaries, lake ice thickness, surface water area, and the specification of watershed runoff coefficients. Analyses and observations based on data acquired from ground based, airborne and spaceborne platforms, and an evaluation of advantages and limitations of microwave sensors are included.

Ulaby, F. T.↗
NASA NTRS1979

The use of microwave approaches in hydrology

Passive (radiometry) and active (radar) microwave approaches and their application to the study of the earth's hydrologic problem are examined and parameters including soil moisture content, snowpack properties, surface water area and the detection of precipitation overland are studied. Results show that these methods are capable of monitoring the moisture content in the surface layer of the soil in 5 cm thickness, detecting the presence of liquid water in snow and observing oil slicks. In addition, the methods make it possible to determine the water equivalent of snow packs and to delineate areas of rainfall over land.

Schmugge, T. J.↗
NASA NTRS1980

Microwave approaches in hydrology

The microwave approaches for remote sensing of soil moisture centent, snowpack properties, surface water area, and the detection of precipitation over land are discussed. Both active (radar) and passive (radiometry) approaches are considered, and the advantages of microwave sensing are pointed out, including all-weather capability, especially at the longer wavelengths, and greater penetration depth with optical or infrared sensors. Results obtained from ground-based, aircraft, and spacecraft platforms show that microwave systems can monitor the moisture content in the surface soil layer (5 cm thick), and that passive microwave systems can discriminate between light and heavy snowcover, detect the presence of liquid water in the snow, and qualitatively estimate snow water equivalent.

Schmugge, T. J.↗
NASA NTRS1985

Air-sea interaction with SSM/I and altimeter

A number of important developments in satellite remote sensing techniques have occurred recently which offer the possibility of studying over vast areas of the ocean the temporally evolving energy exchange between the ocean and the atmosphere. Commencing in spring of 1985, passive and active microwave sensors that can provide valuable data for scientific utilization will start to become operational on Department of Defense (DOD) missions. The passive microwave radiometer can be used to estimate surface wind speed, total air column humidity, and rain rate. The active radar, or altimeter, senses surface gravity wave height and surface wind speed.

Source record↗
NASA NTRS1985

Estimation of biophysical properties of forest canopies through inversion of microwave scatterometer data

A method for estimating the biophysical properties of a forest canopy through inversion of microwave scatterometer data is discussed. A C-band scatterometer flown over an aspen site in northern Minnesota during 19 days from May 2 to October 20, 1984, was modified to enable continuous recording of the range of the target. This provided the backscatter cross section as a function of range and was used to study scattering processes within the canopy. The remote estimates of HH, VV, and HV extinction coefficient values agreed well with the estimates obtained with the use of an active radar calibrator.

Pitts, D. E.↗
NASA NTRS1986

Multi-system report integration using blackboards

Blackboards are an Al problem solving methodology. A blackboard system consists of a structured data base (the blackboard) holding input and derived inferences and a collection of procedures for deriving inferences (knowledge sources). Each knowledge source is specialized to operate on some portion of the blackboard. The knowledge sources are invoked opportunistically as the information on the blackboard increases. The methodology is well suited to integrating multiple streams of fully reduced and qualitatively different data such as active radar track reports, passive electronic intelligence reports, and human intelligence reports about enemy intentions. This paper sketches the nature of the blackboard problem solving methodology with an emphasis on those features suiting it to such applications. The sketch is illustrated with examples from a relatively simple multi-system report integration problem. Relevant applications currently under development at Stanford's Knowledge Systems Laboratory are also described.

Delaney, J. R.↗
NASA NTRS1991

Discrete random media techniques for microwave modeling of vegetated terrain

Microwave remote sensing models of vegetated terrain are investigated. The problem is to determine canopy characteristics such as biomass, canopy height, and the moisture of the underlying soil. The report describes a discrete scatter model which has been employed to model backscatter in the active (radar) case and to model brightness temperature in the passive (radiometric) case. The acquisition of ground truth data is discussed, as well as the comparison of theory and experiment. The overall conclusion of the work has been that the discrete scatter model in conjunction with efficient scatter algorithms and the distorted Born approximation is a most appropriate methodology to use for modeling purposes in the microwave region.

Lang, Roger H.↗
NASA NTRS1992

Preliminary analysis of ERS-1 SAR for forest ecosystem studies

An image obtained by the C-band VV-polarized ERS-1 SAR is examined with respect to potential land applications. A scene obtained near noon on August 15, 1991, along the U.S.-Canadian border near Sault Ste. Marie is calibrated relative to an array of trihedral corner reflectors and active radar calibrators distributed across the swath. Extensive contemporaneous ground observations of forest stands are used to predict the radar backscattering coefficient sigma at the time of the SAR overpass using a first-order vector radiative transfer model. These predictions generally agree with the calibrated ERS-1 data to within 1 dB. It is demonstrated that the dynamic range of sigma is sufficient to perform limited discrimination of various forest and grassland communities even for a single-date observation. Furthermore, retrieval of near-surface soil moisture is feasible for grass-covered soils when plant biomass is less than 1 tonne/ha.

Dobson, M. G.↗
NASA NTRS1992

An examination of the assumptions in the POLCAL cross-talk removal algorithm

The POLCAL crosstalk removal algorithm is based on the statistical properties of the image background and does not need any corner reflector or active radar calibrator deployed in the scene. The advantage of being able to remove the crosstalk contamination without using external calibration targets gives rise to the consideration of algorithms based on clutter statistics in polarimetric synthetic aperture radar (SAR) images in more detail. The basic assumption of the POLCAL procedure is the decorrelation of copolarized and cross-polarized backscatter, which is valid for natural targets with azimuthal symmetry. This assumption and others regarding the properties of the imaged surface are examined. An improved version called POLCALII is presented, and its performance is compared with POLCAL.

Zink, M.↗
NASA NTRS2000

STS-99 Crew Activities Report/Flight Day 1 Highlights

Live footage shows the crew, Commander Kevin R. Kregel, Pilot Dominic L. Pudwill Gorie, and Mission Specialists Janet L. Kavandi, Janice E. Voss, Mamoru Mohri and Gerhard P.J. Thiele, seated in the dining room with the traditional cake. The crew is seen performing various pre-launch activities including suit-up, walk out to the Astro-van, and strap-in into the vehicle. Also seen are the retractions of the orbiter access arm and the gaseous oxygen mint hood, main engine start, booster ignition, liftoff, and separation of the solid rocket boosters. The Red Team (first of the dual shift crew) includes Kregel, Kavandi, and Thiele, who are shown conducting jet thruster firings, activating radar instruments, and deploying the boom (mass).

Source record↗
NASA NTRS2001

The Aqua-Aura Train

This talk will focus on the afternoon constellation of EOS platforms and the scientific benefits that arise from this formation. The afternoon EOS constellation or the "A-train" will provide unprecedented information on clouds and aerosols. At 1:30 PM crossing time EOS-Aqua begins the train with the MODIS, CERES and AIRS instruments making aerosol, cloud, radiation budget , temperature and water vapor measurements. AMSR-E will also make total column water measurements. Following Aqua by one minute, Cloudsat will make active radar precipitation measurements as and PICASSOCENA will make lidar measurements of clouds and aerosols. Fourteen minutes later, EOS-Aura will pass through the same space making upper troposphere water vapor and ice profiles as well as some key trace gases associated with convective processes (MLS and HIRDLS). Additional measurements of aerosols will be made by Aura's OMI instrument.

Schoeberl, Mark↗
NASA NTRS2004

Rain, Snow, Hurricanes, and Blizzards: Remote Sensing of Cloud Particles

Hurricanes, blizzards and other weather events are important to understand not only for disaster preparation, but also to track the global energy balance and to improve weather and climate forecasts. For several decades, passive radiometers and active radars on aircraft and satellites have been employed to remotely sense rain rates and the properties of liquid particles. In the past few years the relationships between frozen particles and millimeter-wave observations have become understood well enough to estimate the properties of ice in clouds. This colloquium will start with a broad background of the use of remote sensing of precipitation and then focus on recent research in the estimation of frozen cloud properties, both for ice that will eventually melt into rain and for solid precipitation falling in northern climates. The electromagnetic absorption and scattering properties of liquid rain and frozen particles will be explained. Retrieved cloud particle contents and size distributions for Hurricane Erin (2001 ) and the March 5-6, 2001 New England regional blizzard will be discussed. Future directions and challenges of this work will also be presented.

Gail Skofronick-Jackson↗
NASA NTRS2004

Characteristics and Trade-Offs of Doppler Lidar Global Wind Profiling

Accurate, global profiling of wind velocity is highly desired by NASA, NOAA, the DOD/DOC/NASA Integrated Program Office (IPO)/NPOESS, DOD, and others for many applications such as validation and improvement of climate models, and improved weather prediction. The most promising technology to deliver this measurement from space is Doppler Wind Lidar (DWL). The NASA/NOAA Global Tropospheric Wind Sounder (GTWS) program is currently in the process of generating the science requirements for a space-based sensor. In order to optimize the process of defining science requirements, it is important for the scientific and user community to understand the nature of the wind measurements that DWL can make. These measurements are very different from those made by passive imaging sensors or by active radar sensors. The purpose of this paper is to convey the sampling characteristics and data product trade-offs of an orbiting DWL.

Kavaya, Michael J.↗
NASA NTRS2004

Passive Remote Sensing of Cloud Ice Particles

Hurricanes, blizzards and other weather events are important to understand not only for disaster preparation, but also to track the global energy balance and to improve weather and climate forecasts. For several decades, passive radiometers and active radars on aircraft and satellites have been employed to remotely sense rain rates and the properties of liquid particles. In the past few years the relationships between frozen particles and millimeter-wave observations have become understood well enough to estimate the properties of ice in clouds. A brief background of passive remote sensing of precipitation will be presented followed by a focused discussion of recent research at NASA Goddard Space Flight Center estimating the properties of frozen particles in clouds. The retrievals are for (1) ice that will eventually melt into rain, (2) for solid precipitation falling in northern climates, and (3) cirrus ice clouds. The electromagnetic absorption and scattering properties and differences of liquid rain versus frozen particles will be summarized for frequencies from 6 to 340+ GHz. Challenges of this work including surface emissivity variability, non-linear and under-constrained relationships, and frozen particle unknowns will be discussed. Retrieved cloud particle contents and size distributions for ice above the melting layer in hurricanes, retrieved snowfall rates for a blizzard, and cirrus ice estimates will be presented. Future directions of this work will also be described.

Skofronick-Jackson, Gail↗
NASA NTRS2004

The HYDROS Radiometer/Radar Instrument

The science objectives of the HYDROS mission are to provide frequent, global measurements of surface soil moisture and surface freeze/thaw state. In order to adequately measure these geophysical quantities, the key instrument requirements were determined by the HYDROS science team to be: 1) Dual-polarization L-Band passive radiometer measurements at 40 km resolution, 2) Dual-polarization L-Band active radar measurements at 3 km resolution, and 3) A wide swath to insure global three day refresh time for these measurements (1000 km swath at the selected orbit altitude of 670 km). As a solution to this challenging set of instrument requirements, a relatively large, 6 meter, conically-scanning reflector antenna architecture was selected for the instrument design. The deployable mesh antenna is shared by both the radiometer and radar electronics by employing a single L-Band feed.

freeze thaw↗
NASA NTRS2009

Compact Microwave Fourier Spectrum Analyzer

A compact photonic microwave Fourier spectrum analyzer [a Fourier-transform microwave spectrometer, (FTMWS)] with no moving parts has been proposed for use in remote sensing of weak, natural microwave emissions from the surfaces and atmospheres of planets to enable remote analysis and determination of chemical composition and abundances of critical molecular constituents in space. The instrument is based on a Bessel beam (light modes with non-zero angular momenta) fiber-optic elements. It features low power consumption, low mass, and high resolution, without a need for any cryogenics, beyond what is achievable by the current state-of-the-art in space instruments. The instrument can also be used in a wide-band scatterometer mode in active radar systems.

Savchenkov, Anatoliy↗