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H. D. Toong and D. H. Staelin

Abstract

Ground-based microwave measurements of atmospheric emission at 5 wavelengths near 1 cm have enabled separate determinations of the water vapor and liquid water contents of the atmosphere. Observations during a frontal passage, in August 1966, yielded humidity estimates within 10% of conventional measurements, and cloud-type estimates compatible with the cloud structure of normal frontal systems.

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W. H. Ledsham and D. H. Staelin

Abstract

An extended Kalman-Bucy filter has been implemented for atmospheric temperature profile retrievals from observations made using the Scanned Microwave Spectrometer (SCAMS) instrument carried on the Nimbus 6 satellite. This filter has the advantage that it requires neither stationary statistics in the underlying processes nor linear production of the observed variables from the variables to be estimated. This extended Kalman-Bucy filter has yielded significant performance improvement relative to multiple regression retrieval methods.

A multi-spot extended Kalman-Bucy filter has also been developed in which the temperature profiles at a number of scan angles in a scanning instrument are retrieved simultaneously. These multi-spot retrievals are shown to outperform the single-spot Kalman retrievals.

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K. S. Nathan, P. W. Rosenkranz, and D. H. Staelin

Abstract

Satellite-borne radiometers have been used with increasing success to monitor geophysical parameters. The majority of the statistical retrieval schemes currently in use for estimating atmospheric temperature profiles are one-dimensional (1-D), that is, they consider correlations only in the dimension perpendicular to the surface. Here, a two-dimensional (2-D) spatial filter, optimum in the minimum-mean-square error sense, is used to retrieve atmospheric temperature profiles from Microwave Sounder Unit measurements. Horizontal correlations along the orbital track are taken into account. This additional statistical information results in lower mean-square errors for the 2-D filter compared to that of its 1-D counterpart. The previously unstudied behavior of retrieval errors as a function of spatial frequency along the orbital track is also investigated. A large part of the improved performance of the 2-D filter is due to the reduction of short spatial wavelength components in the error. In addition, retrievals were carded out over a severe cold front. The 2-D technique yielded substantially lower errors than the 1-D approach. The latter does not perform so well over fronts because of the loss in vertical correlation due to the presence of layers of air with different lapse rates.

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Ali D. S. Ali, Philip W. Rosenkranz, and David H. Staelin

Abstract

The thermal emission spectrum of the atmosphere near the 118 GHz oxygen resonance has been measured from the NASA Convair-990 aircraft as it flew over clear air and storms. The instrument viewed the ground 45° from nadir with a 7.5° beamwidth. Brightness temperatures were measured in six bands 200 MHz wide centered at frequencies 821–1891 MHz from the line at 118.7505 GHz. The double-sideband super-heterodyne receiver had ∼1 K sensitivity for 1 s integration. Comparison of observed clear air brightness temperatures (from 238 mb) with those computed for a coincident dropsonde yielded agreement within 1.4 K; the retrieved temperature profile agreed with the dropsonde with an average magnitude error of 1.4 K. Observations over precipitation yielded brightness perturbations as large as 30 K.

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P. W. Rosenkranz, M. J. Komichak, and D. H. Staelin

Abstract

Simultaneous measurements of microwave emission from the earth, in the oxygen band near 60 GHz and the water vapor line near 183 GHz, permit inference of atmospheric temperature as a function of two variables: pressure and water vapor burden (integrated water vapor content above any level). Combination of these two profiles yields a profile of water vapor burden versus pressure. Occasional singularities in these retrievals can readily be identified and excluded. Numerical simulations have been made, using temperature and water vapor profiles from subtropical and midlatitude radiosonde stations, and assuming surface reflectivities typical of either land or ocean. Over a land surface, the residual rms errors in estimated water vapor burden profile between 300 and 1000 mb, range from 23 to 43% of the a priori standard deviation of water vapor burden for the corresponding climate. The relative humidity profile was also estimated with rms errors ranging from 4 to 17% of saturation. Over a seawater surface, using three additional channels at 18.5, 22.2 and 31.7 GHz, the corresponding results are 3–46% of a priori standard deviation for water vapor burden and 4–15% rms error for relative humidity.

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J. W. Waters, K. F. Kunzi, R. L. Pettyjohn, R. K. L. Poon, and D. H. Staelin

Abstract

This article discusses remote sensing of atmospheric temperatures with the NEMS microwave spectrometer on the Nimbus 5 satellite, and the accuracy with which atmospheric temperatures can be determined by NEMS. The sensitivity of the NEMS instrument allows measurement of temperature profiles having vertical resolution of the respective NEMS weighting functions (∼10 km) with an rms accuracy of a few tenths of a degree Kelvin for a 16 s integration time. The accuracy of NEMS in estimating atmospheric temperatures at the discrete levels (∼2 km vertical resolution in the lower troposphere) used in the operational numerical model of the National Meteorological Center (NMC) is ∼2 K rms, as determined by comparing NEMS results with ground truth data obtained from the NMC operational analysis and from coincident radiosondes. These accuracies are consistent with the theoretical accuracies expected for NEMS.

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A. J. Gasiewski, J. W. Barrett, P. G. Bonanni, and D. H. Staelin

Abstract

Passive microwave imagine of O2emissions using the 118.75-GHz(1) resonance has been investigated for tropospheric and stratosphere remote sensing of atmospheric temperature and precipitation. An imaging millimeter-wave spectrometer (MTS) using eight double-sideband channels centered around the 118.75-GHz O2 resonance, and including a fixed-beam 53.65-GHz radiometer and video camera was constructed. The MTS collected data during 33 flights of the NASA ER-2 high-altitude aircraft in 1986 during the Genesis of Atlantic Lows Experiment (GALE) and the Cooperative Huntsvilie Meteorological Experiment (COHMEX), yielding the first high spatial resolution microwave images of atmospheric O2 brightness.

The isolated 118-GHz fine offers higher spatial resolution and precipitation sensitivity than O2 lines in the 5-mm band near 60 GHz. The brightness temperature perturbations of clouds in nonprecipitating regions are typically twice as large in the 118-GHz channels relative to comparable 60-GHz channels. However, observations over cirrus anvils show that the 118-GHz brightnesses are not adversely sensitive to some optically opaque cloud cover. Thus, these channels are expected to be useful for temperature sounding in the presence of clouds, although retrieval ambiguities can result from variations in the water vapor profile and surface emissivity. The demonstration of 118-GHz temperature profile retrievals is left for a subsequent paper.

Over deep convective precipitation, 118-GHz brightness temperature images are characterized by decreases of up to 200 K due to strong scattering in the storm core. The amplitudes of the 118-GHz brightness perturbations contain information on the altitude of the cell top. The shape of the 118-GHz spectrum is also suggested to contain altitude information by virtue of the various peaking altitudes of the 118-GHz weighting functions. Precipitation cells observed by the MTS sometimes appear in bands or rows, and have been accompanied by periodic radiance structures.

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M. J. Schwartz, J. W. Barrett, P. W. Fieguth, P. W. Rosenkranz, M. S. Spina, and D. H. Staelin

Abstract

An imaging microwave radiometer with eight double-sideband channels centered on the 118-GHz oxygen resonance was flown on a high-altitude aircraft over a tropical cyclone in the Coral Sea. The measurements clearly resolved an eyewall of strong convection and a warm core within the eye. Brightness temperatures observed within the eye were approximately 10 K warmer than those observed in clear air 100 km or more away. This warming extended somewhat beyond the eyewall in the highest (most opaque) channel. The temperature profile in the eye, central pressure, and convective cell-top altitudes are inferred from the data.

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D. H. Staelin, K. F. Kunzi, R. L. Pettyjohn, R. K. L. Poon, R. W. Wilcox, and J. W. Waters

Abstract

The passive microwave spectrometer on the Nimbus 5 satellite has two channels that measure atmospheric water vapor and liquid water abundances over ocean. Observed water vapor abundances range up to 6 g cm−2 and differ from nearby radiosondes by ∼0.4 g cm−2. Average liquid water abundances over a 300 km observation zone range from −0.01 to 0.2 g cm−2, and have an rms error estimated to be ∼0.01 g cm−2 for most circumstances. These quantitative measurements can be used to construct global maps or to accumulate global statistics.

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D. H. Staelin, A. L. Cassel, K. F. Kunzi, R. L. Pettyjohn, R. K. L. Poon, P. W. Rosenkranz, and J. W. Waters

Abstract

The microwave spectrometer on the Nimbus 5 earth observatory satellite has been used to measure thermal radiation in five frequency bands between 22.235 and 58.8 GHz. Clouds were observed to affect less than 0.5% of the temperature profile soundings. Most such effects occur in the intertropical convergence zone and alter the inferred temperature profile by less than a few degrees Centigrade. These effects are evident as cold spots at 53.65 GHz and can be identified by virtue of their small spatial extent, in contrast to smooth variations characteristic of normal atmospheric temperature fields. These effects at 53.65 GHz are sufficiently well correlated with inferred liquid water abundances that they can be used for detecting major storm systems over both land and sea.

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