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Ruf, C.

Publications and source records attributed to Ruf, C..

12 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

Aquarius: The Instrument and Initial Results

Aquarius was launched on June 10, 2011 aboard the Aquarius/SAC-D observatory and the instrument has been operating continuously since the initial turned-on was completed on August 25. The initial observed antenna temperatures were close to predicted and the first salinity map was released in September. In order to map the ocean salinity field, Aquarius includes several special features such as the inclusion of a scatterometer to provide a roughness correction, measurement of the third Stokes parameter to correct for Faraday rotation, and fast sampling to mitigate the effects of RFI. This paper provides an overview of the instrument and an example of initial results. Details are covered in subsequent papers in the session on Aquarius

Ocean salinity↗
NASA NTRS2011

Getting the GeoSTAR Instrument Concept Ready for a Space Mission

The Geostationary Synthetic Thinned Array Radiometer - GeoSTAR - is a microwave sounder intended for geostationary satellites. First proposed for the EO-3 New Millennium mission in 1999, the technology has since been developed under the Instrument Incubator Program. Under IIP-03 a proof-of-concept demonstrator operating in the temperature sounding 50 GHz band was developed to show that the aperture synthesis concept results in a realizable, stable and accurate imaging-sounding radiometer. Some of the most challenging technology, such as miniature low-power 183- GHz receivers used for water vapor sounding, was developed under IIP-07. The first such receiver has recently been adapted for use in the High Altitude MMIC Sounding Radiometer (HAMSR), which was previously developed under IIP-98. This receiver represents a new state of the art and outperforms the previous benchmark by an order of magnitude in radiometric sensitivity. It was first used in the GRIP hurricane field campaign in 2010, where HAMSR became the first microwave sounder to fly on the Global Hawk UAV. Now, under IIP-10, we will develop flight-like subsystems and a brassboard testing system, which will facilitate rapid implementation of a space mission. GeoSTAR is the baseline payload for the Precipitation and All-weather Temperature and Humidity (PATH) mission - one of NASA's 15 "decadal-survey" missions. Although PATH is currently in the third tier of those missions, the IIP efforts have advanced the required technology to a point where a space mission can be initiated in a time frame commensurate with second-tier missions. An even earlier Venture mission is also being considered.

millimeter-wave↗
NASA NTRS2010

Development, Capabilities, and Impact on Wind Analyses of the Hurricane Imaging Radiometer (HIRAD)

The Hurricane Imaging Radiometer (HIRAD) is a new airborne microwave remote sensor for hurricane observations that is currently under development by NASA Marshall Space Flight Center in partnership with the NOAA Atlantic Oceanographic and Meteorological Laboratory/Hurricane Research Division, the University of Central Florida, the University of Michigan, and the University of Alabama in Huntsville. The instrument is being test flown in January and is expected to participate in the tropical cyclone experiment GRIP (Genesis and Rapid Intensification Processes) in the 2010 season. HIRAD is being designed to study the wind field in some detail within strong hurricanes and to enhance the real-time airborne ocean surface winds observation capabilities of NOAA and USAF Weather Squadron hurricane hunter aircraft currently using the operational Stepped Frequency Microwave Radiometer (SFMR). Unlike SFMR, which measures wind speed and rain rate along the ground track at a single point directly beneath the aircraft, HIRAD will provide images of the surface wind and rain field over a wide swath (approximately 3 x the aircraft altitude) with approximately 2 km resolution. This paper describes the HIRAD instrument and the physical basis for its operations, including chamber test data from the instrument. The potential value of future HIRAD observations will be illustrated with a summary of Observing System Simulation Experiments (OSSEs) in which measurements from the new instrument as well as those from existing instruments (air, surface, and space-based) are simulated from the output of a detailed numerical model, and those results are used to construct simulated H*Wind analyses. Evaluations will be presented on the impact on H*Wind analyses of using the HIRAD instrument observations to replace those of the SFMR instrument, and also on the impact of a future satellite-based HIRAD in comparison to instruments with more limited capabilities for observing strong winds through heavy rain. Potential impact on numerical prediction of hurricane intensity will also be discussed.

Miller, T.↗
NASA NTRS2001

The Aquarius Mission: Sea Surface Salinity from Space

Aquarius is a new satellite mission concept to study the impact of the global water cycle on the ocean, including the response of the ocean to buoyancy forcing and the subsequent feedback of the ocean on the climate. The measurement objective of Aquarius is sea surface salinity, which reflects the concentration of freshwater at the ocean surface. Salinity affects the dielectric constant of sea water and, consequently, the radiometric emission of the sea surface to space. Rudimentary space observations with an L-band radiometer were first made from Skylab in the mid-70s and numerous aircraft missions of increasing quality and improved technology have been conducted since then. Technology is now available to carry out a global mission, which includes both an accurate L band (1.413 Ghz) radiometer and radar system in space and a global array of in situ observations for calibration and validation, in order to address key NASA Earth Science Enterprise questions about the global cycling of water and the response of the ocean circulation to climate change. The key scientific objectives of Aquarius examine the cycling of water at the ocean's surface, the response of the ocean circulation to buoyancy forcing, and the impact of buoyancy forcing on the ocean's thermal feedback to the climate. Global surface salinity will also improve our ability to model the surface solubility chemistry needed to estimate the air-sea exchange of CO2. In order to meet these science objectives, the NASA Salinity Sea Ice Working Group over the past three years has concluded that the mission measurement goals should be better than 0.2 practical salinity units (psu) accuracy, 100 km resolution, and weekly to revisits. The Aquarius mission proposes to meet these measurement requirements through a real aperture dual-polarized L band radiometer and radar system. This system can achieve the less than 0.1 K radiometric temperature measurement accuracy that is required. A 3 m antenna at approx. 600km altitude in a sun-synchronous orbit and 300 km swath can provide the desired 100 km resolution global coverage every week. Within this decade, it may be possible to combine satellite sea surface salinity measurements with ongoing satellite observations of temperature, surface height, air-sea fluxes; vertical profiles of temperature and salinity from the Argo program; and modern ocean/atmosphere modeling and data assimilation tools, in order to finally address the complex influence of buoyancy on the ocean circulation and climate.

Koblinsky, Chester↗
NASA NTRS2001

Combining TOPEX and SeaWinds Data to Refine Models for Ocean Surface Emissivity: Wind Vector Signatures at 18, 21 and 37 GHz

TOPEX Microwave Radiometer (TMR) brightness temperature observations at 18, 21, and 37 GHz have been collocated with near-simultaneous SeaWinds wind vector data as well as with a monthly SST climatological product. The combined data set allows us to study the dependence of ocean surface emissivity (at each frequency) upon both wind speed. Results show clear two-branch wind speed dependence; weak and linear below 6 m/s with an abrupt increase in sensitivity above that point. The analysis also shows that the zenith-directed ocean surface emissivity is polarization dependent above wind speeds of 5-6 m/s with an azimuthal variation related to the wind direction. This last result accords with recent polarimetric radiometer observations collected from aircraft. Implications of these observations to water vapor retrieval algorithms, nadir-viewing polarimetry, and ocean emission modeling will be discussed.

Vandemark, D.↗
NASA NTRS2000

The Dependence of Ocean Surface Emissivity on Wind Vector as Measured with TMR

Global TMR brightness temperature observations at 18, 21, and 37 GHz have been colocated with near-simultaneous SeaWinds wind vector data as well as with a monthly SST climatological product. The combined data allow us to study the dependence of ocean surface emissivity, at each frequency, upon both wind speed and direction. Results show a clear two-branch wind speed dependence; weak and linear below 6 m/s with an abrupt increase in sensitivity above that point. Our analysis also shows that the nadir-view ocean surface emissivity depends on the angle between the wind direction and TMR's antenna polarization orientation.

Tran, N.↗
NASA NTRS1987

A microwave radiometer weather-correcting sea ice algorithm

A new algorithm for estimating the proportions of the multiyear and first-year sea ice types under variable atmospheric and sea surface conditions is presented, which uses all six channels of the SMMR. The algorithm is specifically tuned to derive sea ice parameters while accepting error in the auxiliary parameters of surface temperature, ocean surface wind speed, atmospheric water vapor, and cloud liquid water content. Not only does the algorithm naturally correct for changes in these weather conditions, but it retrieves sea ice parameters to the extent that gross errors in atmospheric conditions propagate only small errors into the sea ice retrievals. A preliminary evaluation indicates that the weather-correcting algorithm provides a better data product than the 'UMass-AES' algorithm, whose quality has been cross checked with independent surface observations. The algorithm performs best when the sea ice concentration is less than 20 percent.

Walters, J. M.↗
NASA NTRS1986

The Electronically Steered Thinned Array Radiometer (ESTAR)

The concept of a thinned array radiometer is described as an alternate to large filled apertures to achieve high resolution imaging from space. The serious limitations of conventional mechanical scanning systems and the practical problems associated with a multiple receiver pushbroom system that utilizes a large antenna are discussed. The thinned array is developed in terms of aperture synthesis techniques used in radio astronomy. Examples of thinned array configurations are presented, and future directions are discussed.

Swift, C. T.↗
NASA NTRS1985

Electronically Steered Thinned Array Radiometer (ESTAR) system design, calibration, and sensitivity

The ESTAR system, an imaging L-band radiometer designed to provide measurements of soil moisture from space, is described. The large aperture size dictated by the resolution requirement (10 km or less) suggests the use of aperture synthesis, and plans to have ESTAR operate in low earth orbit require that the synthesis be performed in the short data acquisition time permitted by satellite motion. Two forms of ESTAR are described. ESTAR-0 is to be an airborne prototype designed for proof of concept; it will image a line of eight adjacent pixels with 8 degree spatial resolution of 0.1 degree Kelvin temperature resolution, given 1 sec integration time. ESTAR-1 is the satellite version to operate from space. A tentative sensor design will image a line of 128 0.5 degree pixels with 2.0 degree K resolution assuming 0.7 sec integration at 700 km altitude.

Ruf, C.↗