摘要:

The URSI (International Union of Radio Science) Commission F convened a symposium and workshop in Israel from May 14 to May 23, 1984, entitled “Frontiers of Remote Sensing of the Oceans and Troposphere from Air and Space Platforms.” The areas of research and application covered by this general topic are very active, indeed, and are undergoing intense development. It was, therefore, a very timely meeting to which it seemed most participants came with a certain sense of anticipation. Preprints of the papers to be presented were available in a bound volume before the symposium asNASA Conference Publication 2

ISSN:0148-0227    

DOI:10.1029/JC091iC02p02219

年代:1986

数据来源: WILEY

摘要:

The verified capabilities and some practical usage of the satellite scatterometer in geophysical data production have demonstrated the value of this instrument. This evaluation of scatterometer ability to measure marine winds includes the scatterometer verification data, the state of the art planetary boundary layer model relating the wind profile in the atmosphere to the surface stress, and the pertinent results of the Storms Response Experiment.

ISSN:0148-0227    

DOI:10.1029/JC091iC02p02221

年代:1986

数据来源: WILEY

摘要:

We present instantaneous and 15‐day time‐averaged fields of surface wind, wind stress, curl of the wind stress, and wind divergence. These fields are derived from the Goddard Laboratory for Atmospheres four‐dimensional analysis/forecast cycle, for the period September 6–20, 1978, using conventional data, satellite temperature soundings, cloud‐track winds, and subjectively dealiased Seasat scatterome

ISSN:0148-0227    

DOI:10.1029/JC091iC02p02233

年代:1986

数据来源: WILEY

摘要:

The development of theQueen Elizabeth IIstorm from 1200 UT on September 9, 1978, to 0000 UT on September 11, 1978, is forecast with a limited‐area, fine resolution (100 km) numerical weather prediction model. Forecasts from initial conditions that include and exclude Seasat scatterometer surface winds are performed. When the Seasat winds are allowed to influence the upper levels of the atmosphere, a large positive impact is foun

ISSN:0148-0227    

DOI:10.1029/JC091iC02p02241

年代:1986

数据来源: WILEY

摘要:

Profiles of retrieved satellite observed temperatures provided to the Israel Meteorological Service (IMS) by the National Environmental Satellite Data and Information Service were used to enhance the specification of atmospheric conditions during three winter periods. Introduction of the satellite data was via three alternative schemes, and the enhanced specifications were used to initialize 48‐hour numerical forecasts with the IMS five‐layer primitive equation model; control forecasts were run in parallel from initial conditions without the satellite data. The study selects one forecast from each period for which discernible impacts on forecast synoptic fields can be attributed to the different initializations. The first two case studies examine the results of only one assimilation scheme and the third relates to all three schemes. Verification of the prognostics show the positive impact of including satellite temperatures in the initialization, but there were also examples of negative imp

ISSN:0148-0227    

DOI:10.1029/JC091iC02p02249

年代:1986

数据来源: WILEY

摘要:

Research applicable to measuring winds with a scatterometer and the subsequent use of the data is briefly summarized. Data that demonstrate that (Ū(λ/2)/C(λ)) − 1, which is a quantity closely related to the normal stress, is more closely correlated to the nondimensionalized wave spectrum atLband, (ϕ(ω)ω5/g2), than either Ū(19.5) oru*, which is related to the shear stress, are given. The SOS wind recovery algorithm is shown to fail for light winds (given the power law assumption) and to bias climatological wind data. The data from a scatterometer are far too dense to be used in a synoptic scale analysis. Properties of superobservations to be used for synoptic scale analyses at a 1° resolution are derived and shown to produce very accurate wind fields, given that the scatterometer winds are correct. Superobservations are shown to yield reliable estimates of the horizontal component of the divergence and the curl of the wind stress. Disadvantages of a plus or minus 3‐hour data window for scatterometer data assimilation ar

ISSN:0148-0227    

DOI:10.1029/JC091iC02p02263

年代:1986

数据来源: WILEY

摘要:

This study reveals that the power‐law form of the Seasat A scatterometer system (SASS) empirical backscatter‐to‐wind model function (SASS 1), when combined with the sum‐of‐squares (SOS) wind retrieval algorithm, does not uniformly meet the instrument performance specification requirements. Analysis indicates that the horizontally polarized (Hpol) and vertically polarized (Vpol) components of the benchmark SASS 1/SOS wind retrieval system relating signal strength (backscatter) to wind speed yield self‐consistent results only for a small mid‐range of speeds at larger incidence angles and for a somewhat larger range of speeds at smaller incidence angles. An approach is presented that differs from previous calibration studies: here the internalVpolversusHpolconsistency of the model is examined by the use of a set of pairwise collocated SASS‐produced winds, where one member of a wind pair (UVV) derives from onlyVpolbackscatter measurements and the other (UHH) from onlyHpolmeasurements. This data set was created by extracting from the Seasat mission Geophysical Data Record (GDR) data base all pairs of SASS winds of the form (UVV,UHH) such thatUVVandUHHare observations separated by no more than 5 min and 50 km. The set contains 377,289 such pairs. Comparisons of SASS 1/SOS derived wind data with wind data taken off the coast of Scotland during JASIN and with wind data from NDBO buoys off the U.S. Atlantic, Pacific, and Gulf coasts further underscores the shortcomings of the SASS 1/SOS wind retrieval system. These in situ wind comparisons to SASS indicate geographical differences in the retrieved scatterometer winds that are potentially attributable to environmental differences such as sea surface temperature. Taken together, the in situ comparisons to SASS, and the SASSHpoltoVpolwind intercomparison indicate that the SASS 1/SOS wind retrieval system appears deficient in retrieving some winds, particularly from backscatter measurements made at higher incidence angles. We also find thatHpolbackscatter measurements show greater sensitivity thanVpolbackscatter measurements to wind speed variations above 10 m s−1, while the reverse holds for wind speeds less than 10 m s−1. It should be emphasized that it is the geophysical algorithms that lead to the errors cited here, not the instrumentation or the principles of scatterometry. In displaying these sources of error we have been obliged to outline the algorithmic methodology in a manner of presentation not previously attempted either in the published literature or in the voluminous code documentations. We hope that this material will be of value in itself to users of scatterometer data who seek to enhance their understanding of how su

ISSN:0148-0227    

DOI:10.1029/JC091iC02p02273

年代:1986

数据来源: WILEY

摘要:

Improved second generation normalized radar cross section (NRCS) and brightness temperature (TB) models and associated wind retrieval algorithms are derived for the Seasat microwave radiometer SMMR and scatterometer SASS. The derivation of the NRCS model is based on the assumption of a Rayleigh distribution of wind speeds, and no in situ anemometer measurements are used. Furthermore, the NRCS model derivation is designed to preclude, as much as possible, systematic errors in the polarization and incidence angle relationships. A constant power law NRCS model is used, except for nadir observations. The nadir NRCS for winds above 15 m/s falls off faster with increasing wind speed than is predicted by a constant power law relationship. The TBmodel derivation consists of finding the wind‐induced emissivity coefficients, modifying the 37‐GHz atmospheric absorption coefficients and removing biases in the TBobservations. The TBbiases are found to be stable except for the 18‐GHz channels, which experience large, time‐dependent biases. The NRCS and TBmodels are incorporated into new wind retrieval algorithms, which are used to process the SASS and SMMR 3‐month data sets. Small residual systematic errors in the SASS winds (±0.5 m/s or less) are found. A histogram of the SASS winds closely resembles a Rayleigh distribution. The SASS winds are compared with 1623 National Data Buoy Office (NDBO) buoy observations, and a 1.6‐m/s rms discrepancy, with a −0.1‐m/s bias, is found. The SASS and SMMR winds are compared on a 150‐km cell‐by‐cell basis, giving 123,000 wind comparisons for the 3‐month period. The comparisons are done using eight different combinations of three SMMR channels. Good agreement is found between the SASS and SMMR winds, except for two of the channel combinations that show little, if any, skill in retrieving wind. Over the SASS primary off‐nadir swath, the SMMR and SASS wind agreement ranges from 1.3 to 2.2 m/s, depending on the channel combination. For the SMMR versus SASS nadir wind comparisons, the agreement slightly degrades. The SMMR winds appear to be more noisy than the SASS winds for winds below 3 m/s. These results indicate that the Special Sensor Microwave Imager (SSM/I), to be launched in 1986, will have the capability to measure the near‐surface wind speed t

ISSN:0148-0227    

DOI:10.1029/JC091iC02p02289

年代:1986

数据来源: WILEY

摘要:

An intensive analysis of the vector wind field of one Seasat data set: pass 1339 is described. Wind speed and direction signatures are found in Seasat SAR (synthetic aperture radar) images, and the resulting estimates are compared with the Seasat‐A scatterometer system (SASS) and simultaneous NOAA P‐3 aircraft measurements. A power law is presented to relate SAR‐measured backscatter to SASS‐estimated wind speed, and the SAR estimates are shown to agree with the SASS estimates to within a standard error of 0.7 m/s over a range of wind speeds from 3 m/s to 13 m/s. The surface expressions of atmospheric roll vortices are apparent in several of the SAR images and may be responsible for the wind‐direction signature in these cases. Wind field estimates averaged over regions of variable sizes are possible because of the high resolution of SAR imagery. A method for extracting low wave number directionality and its variability from SAR spectra is described, and SAR direction estimates obtained from spectra of 6.4‐km‐square images are shown to have a precision of approximately 10°. Although a comparison data set that could validate these higher resolution estimates is lacking, averages over 40‐km‐square regions are in good agreement with the other wind field information. The SAR wind direction estimates yield a more complete interpretation in a region with a turning wind field near a front that is ambiguous with only SASS observations. In this region the flow patterns of the high‐resolution estimates appear consistent with our knowledge of the overall circulation, considering all the observations. However, in another region the small‐scale variability is too large and random to represent real wind variability, although averages derived from these estima

ISSN:0148-0227    

DOI:10.1029/JC091iC02p02308

年代:1986

数据来源: WILEY

摘要:

Rain rates, wind speeds, and vertically integrated values of both atmospheric water vapor and cloud liquid water content were obtained from the brightness temperatures measured by the Scanning Multichannel Microwave Radiometer (SMMR) on the Nimbus 7 satellite during the winter of 1979. We examine their spatial relationship to wintertime midlatitude cyclones and a shortwave trough over the North Pacific Ocean as they approach the west coast of North America. Cold fronts are found to be located near the edge of the strongest gradient in integrated atmospheric water vapor. The rain rates exhibit patterns that bear a strong relationship both to the shortwave trough and to the cold fronts. Mesoscale features such as frontal undulations and rain cells are indicated in the rain rate data, even though the sensor resolution is marginal for such features. Rain rates are in reasonably good agreement with rain gage measurements on the coast. Furthermore, the onset of rain on the coast agrees with the timing found by simple advection of the SMMR observed rain areas, suggesting their possible future use in forecasting the timing of coastal rain events. Wind speeds ranging from 5 to 15 m/s in a region surrounding a cold front agree with surface observations. Cloud liquid water content exhibits patterns that are consistent with the frontal cloud patterns and with the analysis of the shortwave position.

ISSN:0148-0227    

DOI:10.1029/JC091iC02p02321

年代:1986

数据来源: WILEY