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Martin, D. W.

Publications and source records attributed to Martin, D. W..

12 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Severe storm detection with passive 37 GHz observations

The research objective was to determine the information content of satellite passive 37 GHz brightness temperatures on the severity of thunderstorms through the measurement of the attenuation (scattering) signature of precipitation. The severe storm detection potential of satellite-observed passive 37 GHz radiances was evaluated by comparing Nimbus-7 Scanning Multi-channel Microwave Radiometer (SMMR) data to reports of severe weather contained in the NSSFC severe weather log for calendar years 1979 and 1980 over the United States east of the Rocky Mountains. Heavy thunderstorms have a characteristic signature in the form of localized very low 37 GHz T sub B from scattering by precipitation-size ice particles (thick cirrus being transparent at this frequency). The local noon and midnight snapshots taken by the SMMR on alternating days (with incomplete areal coverage of the U.S. on any given day) were scanned to find cases of strong scattering by precipitation, revealed by large differences between the 18 and 37 GHz brightness temperatures, the 37 GHz T sub B being at least 20 C lower than the 18 GHz T sub B. The value of the 37 GHz T sub b was then compared to severe weather reports within one hour of the SMMR observation time, in the vicinity of the SMMR-observed storm. It was found that the degree to which the T sub B were lowered was a fairly good indicator of the probability that the storm was severe. Of 263 storms observed by the SMMR during 1979 and 1980, 54 percent had severe weather associated with them for a T sub b below 203 K, while 8 percent of those above this threshold were severe.

Spencer, R. W.↗
NASA NTRS1985

Satellite microwave observations of a storm complex: A comparative analysis

The hypothesis that cold events correspond to a particular stage in a class of thunderstorms was tested. That class is a storms class which updrafts are: (1) strong, broad and moist, and (2) extend well above the freezing level. Condition (1) implies strong mesoscale forcing. Condition (2) implies a tall updraft or a relatively low freezing level. Such storms should have big, intense radar echoes and cold, fast-growing anvils. The thunderstorm events were analyzed by radar, rain gauge and GOES infrared observations. Radar was the starting point for detection and definition of the hypothesized thunderstorms. The radar signature is compared to the signature of the storm in rain gauge observations, satellite infrared images and satellite microwave images.

Martin, D. W.↗
NASA NTRS1983

Satellite microwave radiances correlated with radar rain rates over land

The characteristics of upwelling microwave radiation from raindrops as measured by satellite sensors are examined. The scanning multichannel microwave radiometers on board the Nimbus 7 and Seasat satellites have the capability of quantifying the perpendicularly polarized antenna temperatures at 37, 21, 18, 10.7, and 6.6 GHz. The instruments scan the earth at a constant 50 deg angle to the surface with a footprint that varies from 20-70 km. Radar rainfall measurements have an accuracy of within 60 percent, whereas a series of test measurements using SMMR data in comparison with radar data for rainfall in the same areas showed that the microwave data depicted rainfall rates with less than 1.55 mm/h error. Details of the rainfall rate algorithms used to treat the satellite microwave data are provided, noting that the identification of rainfall rates is dependent on quantifying the amount the upwelling radiance is reduced due to rainfall.

Spencer, R. W.↗
NASA NTRS1983

Heavy thunderstorms observed over land by the Nimbus 7 scanning multichannel microwave radiometer

Brightness temperatures obtained through examination of microwave data from the Nimbus 7 satellite are noted to be much lower than those expected on the strength of radiation emanating from rain-producing clouds. Very cold brightness temperature cases all coincided with heavy thunderstorm rainfall, with the cold temperatures being attributable to scattering by a layer of ice hydrometeors in the upper parts of the storms. It is accordingly suggested that brightness temperatures observed by satellite microwave radiometers can sometimes distinguish heavy rain over land.

Spencer, R. W.↗
NASA NTRS1981

A life history method for estimating convective rainfall

The remote sensing of rain amounts is of great interest for a great variety of operational applications, including hydrology, hydroelectricity and agriculture is discussed. The microwave radiometer represents the most obvious technique, however, poor spatial and temporal resolution, together with the problems associated with the estimation of effective rain layer height make visible and IR techniques more promising at the present time. Based on bivariate frequency distribution of brightness versus temperature, brightness enhancing or infrared technique alone may be inadequate to deduce details of convective activity. It is implied that better estimates of rainfall will come from visible and IR observations combined than from either used alone. The technique identifies clouds with high probability of rain as those which have large optical and presumably physical thickness as measured by the visible albedo in comparison with their height, determined by the intensity of the IR emission.

Martin, D. W.↗
NASA NTRS1980

Deep convection on day 261 of GATE

The structural features of the deep convection observed on September 18, 1974, day 261 of the GARP Atlantic Tropical Experiment (GATE), as the ridge axis of a 700 mb wave passed the center of the GATE B-scale network are reported. Satellite and aircraft maps indicate the presence of clouds penetrating above 2.5 km into the middle troposphere organized in bands about 9 km apart and aligned roughly along the direction of the wind shear in the cloud layer. Radar echoes corresponding to cumulus convection of lifetime, peak height and peak rainfall rates on the orders of 30 min, 6 km and 1.3 mm/h, respectively, were observed to triple in number density as convergence at 950 hPa increased from 1.5 to 3 x 10 to the -5th/sec. The structural features of the radar echoes indicate that the day was similar to a mesoscale precipitation feature of Leary and Houe (1979), with the cluster consisting of many echoes appearing in succession. Data from aircraft penetrations of the deep convection reveal downdrafts accompanying the precipitation and updrafts immediately to their south. Shipboard and rawinsonde observations show that the convective downdrafts brought down air of low pseudo-equivalent potential temperature, with local surface convergence of up to 0.001/sec. Mean wind shears through the cloud layer to the top of a main cloud layer are found to be only 75% greater than those of Malkus (1958) for the Caribbean, with shears just above the cloud base several factors larger.

Warner, C.↗
NASA NTRS1979

Shallow convection on day 261 of GATE - Mesoscale arcs

Cloudy convection in the moist layer of a cloud cluster growing in the GATE ship array is examined. Analyses suggest that the moist layer was dominated by features of horizontal dimension roughly 40 km and lifetime roughly 2 h, with arc patterns triggered by dense downdraft air accompanying rainfall, and composed of many small cumulus clouds. Aircraft recorded data on thermodynamic quantities and winds, indicating that the arcs persisted as mesoscale circulations driven by the release of latent heat in the clouds, rather than being driven by the original density current at the surface. It is also suggested that the mesoscale cloud patterns of the moist layer play a primary role in heat transfer upward within this layer, and contribute to the forcing of showering midtropospheric clouds.

Warner, C.↗
NASA NTRS1979

Estimating GATE rainfall with geosynchronous satellite images

A method of estimating GATE rainfall from either visible or infrared images of geosynchronous satellites is described. Rain is estimated from cumulonimbus cloud area by the equation R = a sub 0 A + a sub 1 dA/dt, where R is volumetric rainfall, A cloud area, t time, and a sub 0 and a sub 1 are constants. Rainfall, calculated from 5.3 cm ship radar, and cloud area are measured from clouds in the tropical North Atlantic. The constants a sub 0 and a sub 1 are fit to these measurements by the least-squares method. Hourly estimates by the infrared version of this technique correlate well (correlation coefficient of 0.84) with rain totals derived from composited radar for an area of 100,000 sq km. The accuracy of this method is described and compared to that of another technique using geosynchronous satellite images. It is concluded that this technique provides useful estimates of tropical oceanic rainfall on a convective scale.

Stout, J. E.↗
NASA NTRS1976

Wind sets from SMS images - An assessment of quality for GATE

The paper analyzes the accuracy, representativeness, and reproducibility of tracer winds in the 1974 GARP Atlantic Tropical Experiment whose data are used as ground truth. The tracer winds were generated by tracking clouds in SMS (Synchronous Meteorological Satellite) images. Data availability limits comparisons to satellite winds with ship winds at the surface and at 250 mb. Attention is focused on how accurately the cloud displacements can be measured and on the extent to which the cloud displacements represent the wind field. Operator errors in obtaining the cloud displacements are examined in a series of reproducibility tests and wind sets. Differences between proximate satellite and ship winds were all under 3 m/sec. Representativeness of cloud tracers for cumulus and cirrus level flow is found to be good within the accuracy of currently available ground truth data.

Suchman, D.↗
NASA NTRS1972

A review of multidisciplinary case studies on the impact of meteorological satellites

Case studies relating to the benefits of satellite meteorology are summarized in a series of tables. Data cover: (1) general areas within the process or operation being studied, (2) weather sensitive factors within general areas, (3) meteorological parameters which control individual factors and their time scale, and (4) meteorological parameters which are judged to be controlling. Meteorological variables and the extent to which they can be inferred by means of present satellite sensors are given.

Martin, D. W.↗