Engineering topics

Spencer, Roy W.

Publications and source records attributed to Spencer, Roy W..

At least 37 records · Page 2

NASA NTRS1993

Global oceanic precipitation from the MSU during 1979-91 and comparisons to other climatologies

The construction and general features of a new monthly oceanic precipitation data set compiled from Microwave Sounding Unit (MSU) data gathered by TIROS-N satellites are described. Rainfall is estimated from the intensity of warming in MSU channel 1 (50.3 GHz) brightness temperatures above a 15-percent cumulative frequency distribution threshold after correction for airmass temperature. The average channel 1 warming above the threshold is calibrated into precipitation units with five to ten years of monthly accumulations from 132 raingages distributed around the globe. Comparisons between the satellite and raingage measurements of the average annual cycle in monthly precipitation are presented for 75 raingages from different climatic regions.

Spencer, Roy W.↗

NASA NTRS1993

Precision lower stratospheric temperature monitoring with the MSU - Technique, validation, and results 1979-1991

The stability of TIROS-N Microwave Sounding Unit (MSU) channel 4, which monitors the deep-layer averaged temperature of the lower stratosphere, is tested by intercalibrating MSU channel 4 data from the NIROS-N series of NOAA satellites during 1979-1991. The monthly gridpoint anomalies are validated with 10 years of radiosonde data during 1979-1988. The results demonstrated that the satellite sensors are very stable in their calibration and that the previously reported uncertainties in the stratospheric temperature information produced by NOAA are not the result of calibration changes in the MSUs. It was found that the largest globally averaged temperature variations during 1979-1991 occur after the El Chichon (1982) and Pinatubo (1991) volcanic eruptions. These warm events are superimposed upon a net downward trend in temperatures during the period. The cooling trend is strongest in polar regions and the Northern Hemisphere middle latitudes.

Spencer, Roy W.↗

NASA NTRS1993

Global temperature variations

Lower stratospheric temperature anomalies from MSU channel 4 were compared to ten years of radiosonde data to validate the satellite record, and the results were submitted for publication. Various assumed stratospheric weighting profiles were tested to determine whether the theoretical channel 4 weighting function had significant errors. It was found that the real weighting function is slightly sharper than the theoretical weighting function. We also found evidence for a step-function cooling in the radiosonde record during 1982, a period when two satellites were operating with no evidence of changes in the satellites. Lower tropospheric bulk temperature datasets continue to be sent to climate researchers and modelers, as well as to the Climate Analysis Center (CAC). The CAC is also implementing our MSU software to be able to do the MSU processing at their site. Drift in MSU channel 3 is being quantified and corrected to allow it to be used together with channel 2 for a better lowertropospheric gridpoint temperature product. A new global oceanic precipitation dataset has been produced from MSU channel 1 data, and compared to ten years of global raingage data.

Spencer, Roy W.↗

NASA NTRS1993

AMPR/SSMI data comparisons

The AMPR was flown during CAPE and STORMFEST, during which some good data were gathered. Significant instrument noise problems were encountered in both deployments which appear to be temperature related. These are being fixed before the TOGA COARE deployment. New calibration loads have also been manufactured for the TOGA COARE configuration. Eric Smith at FSU had been analyzing the AMPR data and has written a journal article to be submitted early this summer. The emphasis of his work is on the interpretation of low resolution microwave data from space, based upon what we have learned from the high-resolution AMPR signatures.

Spencer, Roy W.↗

NASA NTRS1992

Precision and radiosonde validation of satellite gridpoint temperature anomalies. I - MSU channel 2. II - A tropospheric retrieval and trends during 1979-90

Monthly 2.5-deg gridpoint anomalies in the Tiros-N satellite series Microwave Sounding Unit channel 2 brightness temperatures during 1979-1988 are evaluated with multiple satellites and radiosonde data for their climate temperature monitoring capability. The MSU anomalies are computed about a 10-yr mean annual cycle at each gridpoint, with the MSUs intercalibrated to a common arbitrary level. The monthly gridpoint anomaly agreement between concurrently operating satellites reveals single-satellite precision generally better than 0.07 C in the tropics and better than 0.15 C at higher latitudes. The removal from channel 2 of the temperature influence above the 30-kPa level is addressed, providing a sharper and thus potentially more useful weighting function for monitoring lower tropospheric temperatures.

Spencer, Roy W.↗

NASA NTRS1992

Monitoring Global Temperatures From Satellites

Report provides evidence that passive microwave radiometry from satellites provides more-precise information on atmospheric temperatures than sparse distribution of thermometers. Accurate temperatures needed for detection of "greenhouse" warming, evaluation of computer models of change in climate, and for understanding important factors in climate system.

Spencer, Roy W.↗

NASA NTRS1991

AMPR/SSMI data comparisons

The AMPR (Advanced Microwave Precipitation Radiometer) was flown for the first time with successful data collection over precipitation targets in Florida and off the Oregon coast. The AMPR met its expected performance levels with very low noise and relatively troublefree operation. Numerous rain cloud systems over land and ocean were overflown and the measurements at 10.7, 19.35, 37.1, and 85.5 GHz reveal a wide variety of microphysical conditions which exist within rain cloud systems. Although predicted by radiative transfer model calculations from cloud model simulations, this diversity was not observed before due to the poor spatial resolution of spaceborne microwave radiometers. Saturation of the 19.35 GHz rain emission signal was frequently observed in the oceanic rain systems, supporting the desirability of a 10 GHz channel on the TRMM (Tropical Rain Measuring Mission) microwave radiometer for sensitivity to the higher rain rates.

Spencer, Roy W.↗

NASA NTRS1991

Global temperature variations

Intercalibration statistics of all Microwave Sounding Units (MSUs) operating through 1990 were computed and brightness temperature anomalies on various space and time scales were compiled for MSU channels 2 (troposphere) and 4 (lower stratosphere). A tropospheric retrieval was developed through combination of channel 2 data from various view angles across the MSU scan swath to achieve cancellation of the influence of the lower stratosphere, and much of the upper troposphere, on that channel. Radiosonde validation of the MSU channel 2 and tropospheric retrieval anomalies was performed with 10 years of data at all U.S. controlled stations.

Spencer, Roy W.↗

NASA NTRS1991

The advanced microwave precipitation radiometer: A new aircraft radiometer for passive precipitation remote sensing

Past studies of passive microwave measurements of precipitating systems have yielded broad empirical relationships between hydrometeors and microwave transmission. In general, these relationships fall into two categories of passive microwave precipitation retrievals rely upon the observed effect of liquid precipitation to increase the brightness temperature of a radiometrically cold background such as an ocean surface. A scattering-based method is based upon the effect that frozen hydrometeors tend to decrease the brightness temperature of a radiometrically warm background such as land. One step toward developing quantitative brightness temperature-rain rate relationships is the recent construction of a new aircraft instrument sponsored by National Aeronautics and Space Administration/Marshall Space Flight Center (NASA/MSFC). This instrument is the Advanced Microwave Precipitation Radiometer (AMPR) designed and built by Georgia Tech Research Institute to fly aboard high altitude research aircraft such as the NASA ER-2. The AMPR and its accompanying data acquisition system are mounted in the Q-bay compartment of the NASA ER-2.

Hood, Robbie E.↗

NASA NTRS1991

A physical interpretation of brightness temperatures observed by the microwave sounding units based upon raobs

Ten years (1979-1988) of Microwave Sounding Unit (MSU) data from five satellites were calibrated and processed using procedures described by Spence and Christy (1990) and Spenser et al. (1990). The data are averaged at one month and 2.5-deg grid resolution, and the monthly anomalies in channel 2 are computed from annual cycles measured at each gridpoint. The anomalies at gridpoints are then compared with anomalies computed from radiosonde data.

Spencer, Roy W.↗

NASA NTRS1990

A preliminary analysis of the covariation of surface and midtropospheric temperatures

Monthly, seasonal, and annual averages of surface temperatures and midtropospheric (850-300 hPa) layer-mean temperatures for a global network of 100 stations are analyzed for the periods 1950-87 and 1979-88. The periods were selected on the basis of available data products. A preliminary analysis of the covariation between surface temperatures and midtroposphere layer-mean temperatures indicates a strong correlation in the winter hemispheres over midlatitudes and a much weaker correlation in most of the tropics. Results are compared with other in-situ data sets and with satellite Microwave Sounding Unit (MSU) data.

Elms, Joe D.↗

NASA NTRS1990

Global atmospheric temperature monitoring with satellite microwave measurements - Method and results 1979-84

This paper describes a method for determining global atmospheric-temperature anomalies by means of satellite microwave radiometry. It is shown that microwave measurements of molecular oxygen thermal emission by the Microwave Sounding Units (MSUs) flying aboard the NOAA-6 and NOAA-7 can be used to monitor tropospheric temperature anomalies on global basis to a high level of precision. Comparisons between monthly MSU-derived hemispheric temperature anomalies with those computed from surface thermometer data show a very good agreement over the United States, although not for the hemispheres, especially the Southern Hemisphere. In this latter case, the poor agreement is ascribed to weaker thermal coupling between the ocean and the deep troposphere than that over the U.S. Annual anomalies for the hemispheres exhibit better correlations than do monthly anomalies.

Spencer, Roy W.↗

NASA NTRS1990

Precise monitoring of global temperature trends from satellites

Passive microwave radiometry from satellites provides more precise atmospheric temperature information than that obtained from the relatively sparse distribution of thermometers over the earth's surface. Accurate global atmospheric temperature estimates are needed for detection of possible greenhouse warming, evaluation of computer models of climate change, and for understanding important factors in the climate system. Analysis of the first 10 years (1979 to 1988) of satellite measurements of lower atmospheric temperature changes reveals a monthly precision of 0.01 C, large temperature variability on time scales from weeks to several years, but no obvious trend for the 10-year period. The warmest years, in descending order, were 1987, 1988, 1983, and 1980. The years 1984, 1985, and 1986 were the coolest.

Spencer, Roy W.↗

NASA NTRS1990

Global atmospheric temperature anomaly monitoring with passive microwave radiometers

The potential of microwave sounding units (MSU) for augmenting the surface-based thermometer record by providing a measurement representing a significant depth of the troposphere is considered. These radiometers measure the thermal emission by molecular oxygen in the atmosphere at different spectral intervals in the oxygen absorption complex near 60 GHz. Brightness temperature variations measured by NOAA-6 and NOAA-7 MSUs during a near-two year period are analyzed and compared with monthly averaged surface air temperature data. It is demonstrated that MSUs, while of limited use for vertical profiling of the atmosphere, provide stable measurements of vertically average atmospheric temperatures, centered at a constant pressure level.

Spencer, Roy W.↗

NASA NTRS1990

Precision intercomparisons between MSU channel 2 and radiosonde data over the United States

Results are presented of an intercomparison between MSU channel 2 Tb and radiosonde data taking both oxygen and water vapor absorption into account. A total of 45 stations covering most of the central and eastern U.S. were included. Precise comparisons (to 0.1 C or better) between MSU Tb and radiosonde-calculated Tb were found to be possible with large numbers of stations and long averaging periods (many months), although they are not sufficient in number to address the previously documented monthly precision of 0.01 C from satellite-satellite intercomparisons. The MSU channel 2 does not have a 1:1 response to atmospheric temperature variations; the response averages about 92 percent. No evidence was found to suggest that procedural or hardware changes in the U.S. radiosonde system have caused any widespread biases between 1980 and 1986.

Spencer, Roy W.↗

NASA NTRS1989

Precipitation retrieval over land and ocean with the SSM/I - Identification and characteristics of the scattering signal

Consideration is given to the use of the Defense Meteorological Satellite Program's Special Sensor Microwave/Imager (SSM/I) to identify precipitation in warm and cold land and ocean environments. It is shown that the polarization diversity of the SSM/I operating at 85.5 GHz makes it possible to discriminate between low brightness temperatures due to surface water bodies and those due to precipitation. The theoretical sensitivity of SSM/I between 19.35 and 8.5. GHz and the polarization correction for water surfaces and the effects of cloud water are discussed. Examples are presented of observational studies using SSM/I for the delineation of precipitation over land and oceans.

Spencer, Roy W.↗

NASA NTRS1989

SSM/I radiances correlated with 15 minute rain gauge data

The relationship between rain rate and the 85.5 and 37 GHz brightness temperature (BT) observations of the Special Sensor Microwave Imager (SSM/I) is examined to develop a BT-rain rate relationship for quantitative mapping of global precipitation using SSM/I data. SSM/I observations of a long-lived rain event over the south-central U.S. in 1987 are compared with digitized rain gage data from the National Climate Data Center. The results show that, for the squall line system studied, the rain gage amounts were well correlated with SSM/I polarization corrected 85.5 GHz BT.

Spencer, Roy W.↗

NASA NTRS1989

SSM/I liquid and frozen precipitation patterns in Hurricane Gilbert

The rain and ice signatures of tropical oceanic precipitation systems obtained with the Special Sensor Microwave Imager (SSM/I) are examined. A method for polarization correction without the F8 SSM/I V85.5 channel is presented. As an example of the methodology, SSM/I imagery is used to study the ice and liquid features of Hurricane Gilbert.

Spencer, Roy W.↗