Benchmarking KDP in rainfall: a quantitative assessment of estimation algorithms using C-band weather radar observations
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Uncertainty in vertically integrated liquid water content due to radar reflectivity observation error
Radar reflectivity is used to estimate meteorological quantities such as rainfall rate, liquid water content, and the related quantity, vertically integrated liquid (VIL) water content. The estimation of any of these quantities depends on several assumptions related to the characteristics of the physical processes controlling the occurrence and character of water in the atmosphere. Additionally, there are many sources of error associated with radar observations, such as those due to brighthand, hail, and drop size distribution approximations. This work addresses one error of interest, the radar reflectivity observation error; other error sources are assumed to be corrected or negligible. The result is a relationship between the uncertainty in VIL water content and radar reflectivity measurement error. An example application illustrates the estimation of VIL uncertainty from typical radar reflectivity observations and indicates that the coefficient of variation in VIL is much larger than the coefficient of variation in radar reflectivity.
French, Mark N.↗
Detection and interpretation of ocean roughness variations across the Gulf Stream inferred from radar cross section observations
Radar cross section data shows that the Gulf Stream has a higher cross section per unit area (interpreted here as a greater roughness) than the water on the continental shelf. A steep gradient in cross section was often seen at the expected location of the western boundary. There were also longer-scale (10-20 km) gradual fluctuations within the stream of significant magnitude. These roughness variations are correlated with the surface shear stress that the local wind imposes on the sea. Using the available surface-truth information concerning the wind speed and direction, an assumed Gulf Stream velocity profile, and high-resolution ocean-surface temperature data obtained by the VHRR onboard a NOAA-NESS polar-orbiting satellite, the present study demonstrates that the computed surface stress variation bears a striking resemblance to the measured radar cross-section variations.
Weissman, D. E.↗
Gravity-wave spectra in the atmosphere observed by MST radar, part 4.2B
A universal spectrum of atmospheric buoyancy waves is proposed based on data from radiosonde, Doppler navigation, not-wire anemometer and Jimsphere balloon. The possible existence of such a universal spectrum clearly will have significant impact on several areas in the study of the middle atmosphere dynamics such as the parameterization of sub-grid scale gravity waves in global circulation models; the transport of trace constituents and heat in the middle atmosphere, etc. Therefore, it is important to examine more global wind data with temporal and spatial resolutions suitable for the investigation of the wave spectra. Mesosphere-stratosphere-troposphere (MST) radar observations offer an excellent opportunity for such studies. It is important to realize that radar measures the line-of-sight velocity which, in general, contains the combination of the vertical and horizontal components of the wave-associated particle velocity. Starting from a general oblique radar observation configuration, applying the dispersion relation for the gravity waves, the spectrum for the observed fluctuations in the line-of-sight gravity-wave spectrum is investigated through a filter function. The consequence of the filter function on data analysis is discussed.
Scheffler, A. O.↗
Doppler effects on velocity spectra observed by MST radars
Recently, wind data from mesophere-stratosphere-troposphere (MST) radars have been used to study the spectra of gravity waves in the atmosphere (Scheffler and Liu, 1985; VanZandt et al., 1985). Since MST radar measures the line-of-sight Doppler velocities, it senses the components of the wave-associated velocities along its beam directions. These components are related through the polarization relations which depend on the frequency and wave number of the wave. Therfore, the radar-observed velocity spectrum will be different from the original gravity-wave spectrum. Their relationship depends on the frequency and wave number of the wave as well as the propagation geometry. This relation can be used to interpret the observed data. It can also be used to test the assumption of gravity-wave spectrum (Scheffler and Liu, 1985). In deriving this relation, the background atmosphere has been assumed to be motionless. Obviously, the Doppler shift due to the background wind will change the shape of the gravity-wave power spectrum as well as its relation with the radar-observed spectrum. Here, researcher's investigate these changes.
Scheffler, A. O.↗
probing the atmosphere with high power, high resolution radars
Observations of radar echoes from the clear atmosphere are presented and the scattering mechanisms responsible for the two basic types of clear-air echoes are discussed. The commonly observed dot echo originates from a point in space and usually shows little variation in echo intensity over periods of about 0.1 second. The second type of clear-air radar echo appears diffuse in space, and signal intensities vary considerably over periods of less than 0.1 second. The echoes often occur in thin horizontal layers or as boundaries of convective activity; these are characterized by sharp gradients of refractive index. Some features of clear-air atmospheric structures as observed with radar are presented. These structures include thin stable inversions, convective thermals, Benard convection cells, breaking gravity waves, and high tropospheric layers which are sufficiently turbulent to affect aircraft.
Hardy, K. R.↗
Assessing Dual-Polarization Radar Estimates of Extreme Rainfall During Hurricane Harvey
Hurricane Harvey hit the Texas Gulf Coast as a major hurricane on August 25, 2017 before exiting the state as a tropical storm on August 29, 2017. Left in its wake was historic flooding, with some locations measuring more than 60 inches of rain over a five-day period. The WSR-88D radar (KHGX) maintained operations for the entirety of the event. Rain gauge data from the Harris County Flood Warning System (HCFWS) was used for validation with the full radar data set to retrieve daily and event-total precipitation estimates for the period August 25-29, 2017. The KHGX precipitation estimates were then compared to the HCFWS gauges. Three different hybrid polarimetric rainfall retrievals were used, along with attenuation-based retrieval that employs the radar-observed differential propagation. An advantage of using a attenuation-based retrieval is its immunity to partial beam blockage and calibration errors in reflectivity and differential reflectivity. All of the retrievals are susceptible to changes in the observed Drop Size Distribution (DSD). No in situ DSD data were available over the study area, so changes in the DSD were interpreted by examining the observed radar data. We examined the parameter space of two key values in the attenuation retrieval to test the sensitivity of the rain retrieval. Selecting a value of α=0.015 and β=0.600 and β=0.625 provided the best overall results, relative to the gauges, but more work needs to be done to develop an automated technique to account for changes in the ambient DSD.
David B Wolff↗
Assessing Dual-Polarization Radar Estimates of Extreme Rainfall During Hurricane Harvey
Hurricane Harvey hit the Texas Gulf Coast as a major hurricane on 25 August 2017 before exiting the state as a tropical storm on 29 August 2017. Left in its wake was historic flooding, with some locations measuring more than 60 in. (150 cm) of rain over a 5-day period. The WSR-88D radar (KHGX) maintained operations for the entirety of the event. Rain gauge data from the Harris County Flood Warning System (HCFWS) was used for validation with the full radar dataset to retrieve daily and event-total precipitation estimates for the period 25–29 August2017. The KHGX precipitation estimates were then compared with the HCFWS gauges. Three different hybrid polarimetric rainfall retrievals were used, along with attenuation-based retrieval that employs the radar-observed differential propagation. An advantage of using a attenuation-based retrieval is its immunity to partial beam blockage and calibration errors in reflectivity and differential reflectivity. All of the retrievals are susceptible to changes in the observed drop size distribution (DSD). No in situ DSD data were available over the study area, so changes in the DSD were interpreted by examining the observed radar data. We examined the parameter space of two key values in the attenuation retrieval to test the sensitivity of the rain retrieval. Selecting a value ofa50.015 andb50.600 provided the best overall results, relative to the gauges, but more work needs to be done to develop an automated technique to account for changes in the ambient DSD.
David Billings Wolff↗
Comparison of satellite IR rain estimates with radar rain observations in hurricanes
Radar-observed rainrates and rain areas obtained for the Hurricanes Frederic (1979), Alicia (1983), and Diana (1984) were used in conjunction with GOES IR data to examine the validity of three satellite IR rain estimation techniques: the Arkin (1983) method, the Negri-Adler-Wetzel (1984) technique, and the convective-stratiform technique of Adler and Negri (1987). The Alicia hurricane was also monitored using the subjective manual technique of Spayd and Scofield (1984). It is shown that the success of IR techniques in identifying areas of rainfall depends on the hurricane feature being addressed. Thus, the three objective IR techniques were unable to identify the locations of radar-observed eyewall and inner band precipitation areas because of strong vertical wind shear in the eyewall and the lack of the vertical extent of stratiform precipitation beneath the central dense overcast.
Morris, K. Robert↗
Imaging radar polarization signatures - Theory and observation
Radar polarimetry theory is reviewed, and comparison between theory and experimental results obtained with an imaging radar polarimeter employing two orthogonally polarized antennas is made. Knowledge of the scattering matrix permits calculation of the scattering cross section of a scatterer for any transmit and receive polarization combination, and a new way of displaying the resulting scattering cross section as a function of polarization is introduced. Examples of polarization signatures are presented for several theoretical models of surface scattering, and these signatures are compared with experimentally measured polarization signatures. The coefficient of variation, derived from the polarization signature, may provide information regarding the amount of variation in scattering properties for a given area.
Van Zyl, Jakob J.↗
Ionospheric footprint of magnetosheathlike particle precipitation observed by an incoherent scatter radar
We have examined Sondrestrom incoherent scatter radar observations of ionospheric plasma density and temperature distributions and measurements of F region ion drifts that were made during a prenoon pass of the Defense Meteorological Satellite Program (DMSP)-F7 satellite through the radar field of view. The spacecraft traversed a region of intense electron precipitation with a characteristic energy below approximately 200 eV. Particles with such low characteristic energies are believed to be directly or indirectly of magnetosheath origin. The precipitation region had a width about 2 deg invariant latitude and covered the low-latitude boundary layer (LLBL), the cusp, and the equatorward section of the plasma mantle (PM). The corotating radar observed a patch of enhanced electron density and elevated electron temperature in the F2 region between about 10.5 and 12 magnetic local time in the same invariant latitude range where DMSP-F7 detected the soft-electron flux. The ion drift pattern, also obtained by radar, shows that it is unlikely that the plasma patch was produced by solar radiation and advected into the radar field of view. We suggest that the radar observed modifications of the ionospheric plasma distribution, which resulted from direct entry of magnetosheath electrons into the magnetosphere and down to ionospheric altitudes. Model calculations of the ionospheric response to the observed electron precipitation support our interpretation. The spectral characteristics of the electron flux in the LLBL, cusp, and equatorward section of the PM were in this case too similar to allow to distinguish between them by using incoherent scatter radar measurements only.
Watermann, Jurgen↗
Estimations of model parameters for gravity wave spectra observed by MST radar
The general theory of MST radar observations of gravity wave spectra is developed. This effort extends the previous results to include anisotropy and Doppler effects for the spectra, as well as the consequences for the multibeam configuration. The relationships between the observed one- or two-dimensional spectra for the line-of-sight velocity in the gravity wave spectra are derived. Expressions for cross spectra, as well as covariances between velocities observed on different beams, are computed. Using these results, studies are carried out to show how model parameters for gravity wave spectra can be estimated from the observed quantities. Model parameters include the variance, power law indices, anisotropy parameters, Doppler parameters, mean scale sizes, etc. Cases with different numbers of beams are investigated.
Scheffler, A. O.↗
Seasat SAR cross-section modulation by surface winds - GOASEX observations
Seasat radar observations of the Gulf of Alaska by the Synthetic Aperture Radar (SAR) and the Wind Speed Scatterometer (SASS) indicate that L-band backscatter is modulated by wind speed and possibly by wind direction. It is noted that the L-band backscatter is approximately proportional to the square root of surface winds and that upwind/crosswind differences in backscatter can be as large as 10% in the range of these wind speeds. It is suggested that Seasat SAR images, in conjunction with Seasat Scatterometer data may provide fine-scale mapping of ocean winds and directions. The need for further Seasat SAR-SASS comparisons in order to extend the range of wind speeds is stressed.
Thompson, T. W.↗
Radio and radar astronomical observations
Radio and radar astronomy investigations at Haystack Observatory
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Radar spectral observations of snow
Radar remote sensing experiments have been conducted at test sites in Kansas, Colorado, and South Dakota over the last six years to examine backscatter coefficient response to snowcovered terrain. Truck-mounted 1-35 GHz scatterometers were employed in conjunction with detailed ground-truth measurements. From these experiments and associated modeling efforts, most of the fundamental questions concerning backscatter behavior in response to important snow parameters have been, at least qualitatively, answered. The optimum angular range seems to be between 20 and 50 deg and, for these angles, the results indicate that the radar backscatter generally: (1) increases with increasing water equivalent, (2) decreases with increasing liquid water, (3) increases with increasing crystal size, (4) is insensitive to surface roughness for dry snow conditions, and (5) can be sensitive to soil state if the snowcover is dry. This paper gives a summary of these results, along with empirical and theoretical models for describing the backscatter from snow.
Stiles, W. H.↗
Combined observations of meteors by image-orthicon television camera and multi-station radar
Observations from multiple sites of a radar network and by television of 29 individual meteors from February 1969 through June 1970 are reported. Only 12 of the meteors did not appear to fragment over all the observed portion of their trajectories. From these 12, the relation for the radar magnitude to the panchromatic absolute magnitude was found in terms of velocity of the meteor. A very tentative fit to the data on the duration of long enduring echoes versus visual absolute magnitude is made. The exponential decay characteristics of the later parts of several of the light curves are pointed out as possible evidence of mutual coalescence of droplets into which the meteoroid has completely broken.
Cook, A. F.↗
Nimbus-7 SMMR precipitation observations calibrated against surface radar during TAMEX
This paper represents a continuation of work begun by Petty and Katsaros (1990) on refining an attenuation-based technique for estimating rainfall parameters from polarized 37-GHz brightness temperatures. In the present work, Nimbus-7 SMMR normalized 37-GHz polarization differences P are compared with surface digital radar observations of oceanic precipitation, made during the Taiwan Area Mesoscale Experiment (TAMEX) for cases when the SMMR and the radar coverages of significant precipitation features were nearly simultaneous. After the radar data were corrected for range-dependent errors, relationships were determined between the 37-GHz P and the radar reflectivity factor Z. The relationship was used to generate a large set of simulated SMMR observations from all available TAMEX radar scans, to produce histograms and mean values of pixel-averaged rain rate as a function of P.
Petty, Grant W.↗
SAR (Synthetic Aperture Radar). Earth observing system. Volume 2F: Instrument panel report
The scientific and engineering requirements for the Earth Observing System (EOS) imaging radar are provided. The radar is based on Shuttle Imaging Radar-C (SIR-C), and would include three frequencies: 1.25 GHz, 5.3 GHz, and 9.6 GHz; selectable polarizations for both transmit and receive channels; and selectable incidence angles from 15 to 55 deg. There would be three main viewing modes: a local high-resolution mode with typically 25 m resolution and 50 km swath width; a regional mapping mode with 100 m resolution and up to 200 km swath width; and a global mapping mode with typically 500 m resolution and up to 700 km swath width. The last mode allows global coverage in three days. The EOS SAR will be the first orbital imaging radar to provide multifrequency, multipolarization, multiple incidence angle observations of the entire Earth. Combined with Canadian and Japanese satellites, continuous radar observation capability will be possible. Major applications in the areas of glaciology, hydrology, vegetation science, oceanography, geology, and data and information systems are described.
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