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About 3,288 papers for “Scatterometer”

Laser Scatterometer

Yi-Sheng Chen, Wen-Gui Wang · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 1989

We research and manufacture an instrument for measuring surface scattering and roughness of supersmooth surfaces. It can be used not only for measuring opaque sample but also for measuring transparent sample.

Cited by 0

Scatterometer Program

W. L. Floyd, T. Lund · IEEE Transactions on Aerospace and Electronic Systems · 1966

The radar backscattering cross-sections of various land and sea surfaces were measured by a unique device called a scatterometer.2 The scatterometer measures radar backscattering of the terrain at all angles of incidence simultaneously by utilizing the doppler spectral density of an airborne radar system. The system was vertically polarized and had a transmitter frequency of 13.3 Gc.

Cited by 1

Digital Beamforming Scatterometer

Racette, Paul, Vega, Manuel, Hillard, Larry et al. · NASA STI Repository (National Aeronautics and Space Administration)

This paper discusses scatterometer measurements collected with multi-mode Digital Beamforming Synthetic Aperture Radar (DBSAR) during the SMAP-VEX 2008 campaign. The 2008 SMAP Validation Experiment was conducted to address a number of specific questions related to the soil moisture retrieval algorithms. SMAP-VEX 2008 consisted on a series of aircraft-based.flights conducted on the Eastern Shore of Maryland and Delaware in the fall of 2008. Several other instruments participated in the campaign including the Passive Active L-Band System (PALS), the Marshall Airborne Polarimetric Imaging Radiometer (MAPIR), and the Global Positioning System Reflectometer (GPSR). This campaign was the first SMAP Validation Experiment. DBSAR is a multimode radar system developed at NASA/Goddard Space Flight Center that combines state-of-the-art radar technologies, on-board processing, and advances in signal processing techniques in order to enable new remote sensing capabilities applicable to Earth science and planetary applications [l]. The instrument can be configured to operate in scatterometer, Synthetic Aperture Radar (SAR), or altimeter mode. The system builds upon the L-band Imaging Scatterometer (LIS) developed as part of the RadSTAR program. The radar is a phased array system designed to fly on the NASA P3 aircraft. The instrument consists of a programmable waveform generator, eight transmit/receive (T/R) channels, a microstrip antenna, and a reconfigurable data acquisition and processor system. Each transmit channel incorporates a digital attenuator, and digital phase shifter that enables amplitude and phase modulation on transmit. The attenuators, phase shifters, and calibration switches are digitally controlled by the radar control card (RCC) on a pulse by pulse basis. The antenna is a corporate fed microstrip patch-array centered at 1.26 GHz with a 20 MHz bandwidth. Although only one feed is used with the present configuration, a provision was made for separate corporate feeds for vertical and horizontal polarization. System upgrades to dual polarization are currently under way. The DBSAR processor is a reconfigurable data acquisition and processor system capable of real-time, high-speed data processing. DBSAR uses an FPGA-based architecture to implement digitally down-conversion, in-phase and quadrature (I/Q) demodulation, and subsequent radar specific algorithms. The core of the processor board consists of an analog-to-digital (AID) section, three Altera Stratix field programmable gate arrays (FPGAs), an ARM microcontroller, several memory devices, and an Ethernet interface. The processor also interfaces with a navigation board consisting of a GPS and a MEMS gyro. The processor has been configured to operate in scatterometer, Synthetic Aperture Radar (SAR), and altimeter modes. All the modes are based on digital beamforming which is a digital process that generates the far-field beam patterns at various scan angles from voltages sampled in the antenna array. This technique allows steering the received beam and controlling its beam-width and side-lobe. Several beamforming techniques can be implemented each characterized by unique strengths and weaknesses, and each applicable to different measurement scenarios. In Scatterometer mode, the radar is capable to.generate a wide beam or scan a narrow beam on transmit, and to steer the received beam on processing while controlling its beamwidth and side-lobe level. Table I lists some important radar characteristics

Cited by 0Open access

Coherent Heterodyne Scatterometer

L.Z. Gacusan, S.L. Kwiatkowski, B.J. Sullivan et al. · 1988

An instrument has been developed that measures the magnitude of the Bidirectional Scattering Distribution Function (BSDF) employing coherent optical heterodyne detection at 633nm in a Mach-Zehnder interferometer configuration. In preliminary measurements, instrument performance agrees with theoretical predictions and is characterized by diffraction limited resolution, 15 decades of dynamic range and shot noise limited sensitivity. The scatterometer is constructed from readily available components and the instrument configuration can be adapted to measure scattering from objects in transmission or reflection. In the scatterometer, the beam from a commercially available stabilized 3mW He-Ne laser is split into two beams: a scattering beam and a local oscillator beam. The frequency of each beam is individually shifted by separate acousto-optic modulators operating at different drive frequencies. The scattering beam is directed to the target whose orientation is adjustable. The scattered light and the local oscillator beam are combined and directed onto a photodetector where the resulting heterodyne signal is the frequency difference between the two beams. The RF power of the heterodyne signal is proportional to the optical power that is scattered from the target and is polarization-and mode-matched to the local oscillator beam. The combination of shot-noise-limited sensitivity of a heterodyne detector and milliwatt saturation levels of typical photodetectors provides the large dynamic range necessary for accurate measurements of BSDF. Moreover, characteristics inherent to coherent detection systems permit measurements with diffraction limited angular resolution and yield information of the polarization content of the scattered light. Results of BSDF measurements of various surfaces and materials will be presented.

Cited by 1

S-1 Scatterometer

É. Mougin · 1996

became available only in 1978 with the launch of the Scanning Multichannel Microwave Radiometer (SMMR) on board the Nimbus-7 satellite, and since 1987 with the Spatial sensor ~i~~~~~~~ I~~~~~ (SSMI). Indices, based on the difference recorded at 37 GHz, have been related to canopy water con

Cited by 0

Ring laser scatterometer

Mark R. Ackermann · OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information) · 2023

A scatterometer utilizes the dead zone resulting from lockup caused by scatter from a sample located in the optical path of a ring laser at a location where counter-rotating pulses cross. The frequency of one pulse relative to the other is varied across the lockup dead zone.

Cited by 0Open access

Scatterometer constellation and extremes

Stoffelen, Ad, Vogelzang, J., Giesen, Rianne et al. · DIGITAL.CSIC (Spanish National Research Council (CSIC)) · 2021

Third International Workshop on Satellite Analysis of Tropical Cyclones (IWSATC-3), 7-10 December 2021

Cited by 0

The SeaWinds scatterometer instrument

Chialin Wu, J.E. Graf, Michael H. Freilich et al. · 2002

The SeaWinds scatterometer instrument is currently being developed by NASA/JPL, as a part of the NASA EOS Program, for flight on the Japanese 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. The SeaWinds pencil-beam-antenna conical-scan design is a change from the fixed fan-beam antennas of SASS and NSCAT. The purpose of this change is to develop a more compact design consistent with the accommodation constraints of the ADEOS II spacecraft. The SeaWinds conical-scan arrangement has a 1-m reflector dish antenna that provides a time shared dual-antenna beam at 40 and 46 degree look angles. The dual-beam operation provides up to four azimuth look directions for each wind measurement cell. At an orbit height of 803 km, the conical scan provides a broad and contiguous wind measurement swath of about 1800 km for each orbit pass. Radiometric measurement performance from a conical scan is inherently stable because of a common antenna apparatus, a measurement cell well defined by the narrow antenna beamwidth, and only two fixed-beam incidence angles for the multiple azimuth looks. A tracking filter is required to accommodate variations in the Doppler shift of the echo during the scan period. Key specifications of the SeaWinds instrument and associated tradeoffs and performance are described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Cited by 27

Scatterometer data analysis techniques

H. W. Masenthin · NASA Technical Reports Server (NASA) · 1967

Radar scatterometry programs in the past have been almost entirely motivated by the need for radar design information.This emphasis has limited both the amount of ground truth information obtained and the development of data interpretation techniques.M o s t of the data obtained in these programs is summarized in scattering crcss section versus angle of incidence curves that are identified by the radar parameters and relatively gross descriptions of the surface (New Jersey woods, Lake Michigan, city of Chicago, etc .)

Cited by 2Open access

A Small-Angle Scatterometer

Steven J. Wein, William L. Wolfe · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 1989

The design, analysis, and performance of a small-angle scatterometer are presented. A dye-cell Gaussian apodized aperture is utilized to reduce the small-angle diffraction background. After the diffraction background is sufficiently reduced, the system scatter becomes the dominant noise in the instrument beam profile. The geometrical aberrations are graphically shown to have no significant effect on the higher-order diffraction rings of the beam profile, and as such, an aberrational tolerancing approach can be employed in scatterometer design. Small-angle scattered light measurements are presented for two mirror samples. The associated beam profiles and NEBRDF levels are also given.

Cited by 6

Global scatterometer wind resource

IAN YOUNG, Kirezci, Ebru, AGUSTINUS RIBAL · University of Melbourne data repository · 2020

A 27-year-long calibrated multi-mission scatterometer data set is used to determine the global basin-scale and near-coastal wind resource. In addition to mean and percentile values, the analysis also determines the global values of both 50- and 100-year return period wind speeds. The analysis clearly shows the seasonal variability of wind speeds and the differing response of the two hemispheres. The maximum wind speeds in each hemisphere are comparable but there is a much larger seasonal cycle in the northern hemisphere. As a result, the southern hemisphere has a more consistent year-round wind climate. Hence, coastal regions of southern Africa, southern Australia, New Zealand and southern South America appear particularly suited to coastal and offshore wind energy projects. The extreme value analysis shows that the highest extreme wind speeds occur in the North Atlantic Ocean with extreme wind regions concentrated along the western boundaries of the North Atlantic and North Pacific Oceans and the Indian Ocean sector of the Southern Ocean. The signature of tropical cyclones is clearly observed in each of the well-known tropical cyclone basins.

Cited by 0Open access