Low-altitude Coverage Research Articles

Geospatial QPE Accuracy Dependence on Weather Radar Network Configurations

AbstractThe relatively low density of weather radar networks can lead to low-altitude coverage gaps. As existing networks are evaluated for gap fillers and new networks are designed, the benefits of low-altitude coverage must be assessed quantitatively. This study takes a regression approach to modeling quantitative precipitation estimation (QPE) differences based on network density, antenna aperture, and polarimetric bias. Thousands of cases from the warm-season months of May–August 2015–17 are processed using both the specific attenuation [R(A)] and reflectivity–differential reflectivity [R(Z, ZDR)] QPE methods and are compared with Automated Surface Observing System (ASOS) rain gauge data. QPE errors are quantified on the basis of beam height, cross-radial resolution, added polarimetric bias, and observed rainfall rate. The collected data are used to construct a support vector machine regression model that is applied to the current WSR-88D network for holistic error quantification. An analysis of the effects of polarimetric bias on flash-flood rainfall rates is presented. Rainfall rates that are based on 2-yr/1-h return rates are used for a contiguous-U.S.-wide analysis of QPE errors in extreme rainfall situations. These errors are then requantified using previously proposed network design scenarios with additional radars that provide enhanced estimate capabilities. Last, a gap-filling scenario utilizing the QPE error model, flash-flood rainfall rates, population density, and potential additional WSR-88D sites is presented, exposing the highest-benefit coverage holes in augmenting the WSR-88D network (or a future network) relative to QPE performance.

Short-Wavelength Technology and the Potential For Distributed Networks of Small Radar Systems

The NSF Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere (CASA) is advancing a new approach to radar network design based on dense networks of short-range radars. The center's concept is to deploy small radars atop communication towers, rooftops, and other elements of the infrastructure as a means to comprehensively map winds, rainfall, and other atmospheric and airborne objects throughout the atmosphere with resolution, low-altitude coverage, Doppler wind vector measurement, and other capabilities that are substantially beyond the current state-of-the-art. The technology has the potential to supplement - or perhaps replace - the large long-range civil infrastructure radars in use today.

Modeling Mercury's internal magnetic field with smooth inversions

Three-component vector magnetic field observations from MESSENGER's first flyby of Mercury have confirmed the presence of an internal field, along with external fields due to magnetospheric current systems. We use techniques from inverse theory to investigate structure in Mercury's internal magnetic field permitted by the Mariner 10 and MESSENGER flyby data and recoverable from orbit. We correct the flyby observations using external fields predicted by a parameterized magnetospheric model, and we include noise contributions from long-wavelength uncertainties in the external field and from un-modeled short-wavelength features. The internal field is represented by a spherical harmonic expansion to degree and order 8, with regularization constraints applied to the power spectrum. Latitudinal and longitudinal structure in the field is required in order to fit the data. Enhanced radial magnetic field in the region of the Mariner 10 and MESSENGER flyby latitudes is seen. Contributions to the internal field predicted by Aharonson and others for a long-wavelength crustal field are present, but the field is dominated by the g 0 1 term rather than the predicted g 0 3 term. Observations from MESSENGER's second and third flybys will provide additional low-altitude coverage at equatorial latitudes, while the orbital phase of the mission will provide high-latitude, northern-hemisphere coverage. We investigate recovery of three simulated core fields using the cumulative data coverage that will be obtained from the three MESSENGER flybys and MESSENGER's orbital phase, under the assumption that long-wavelength external fields can be modeled and removed. This provides a best-case scenario for internal field modeling. The results show excellent recovery of the dipole field and of field structure at mid to high northern latitudes with spatial scales equivalent to degree and order 10, providing encouraging results for the identification and characterization of core fields.

The MAPSTAR imaging Doppler interferometer (IDI) radar: description and first results

MAPSTAR is a medium-frequency imaging Doppler interferometer (IDI) radar. In this paper we describe the radar and present results from 34.5 h of data taken during the AIDA campaign in Puerto Rico during April 1989. The IDI method uses several independent antennas and receivers, pulsed sounding, range-gating, Doppler sorting and spatial interferometry to determine a three-dimensional Doppler image of the rf scatterers within the volume being illuminated. The analysis characterizes any perturbation in the index of refraction that returns rf energy (clear-air turbulence, scattering from striations, meteor trails, etc.) in terms of the three-dimensional locations, Doppler velocities and scattering amplitudes and phases of a number of apparent points in space, called ‘scattering points’. Scattering points are defined as those Fourier voltages whose phases on the several antennas agree on the direction in the sky of the source of that spectral power. We find that most of the power scattered from the mesosphere and E region can be described in this fashion. This allows us to replace, say, 10 complex voltages by two voltages and two coordinates locating the source. The IDI process is, en passant, a data-compression technique, reducing the data volume by a factor of 25–30 without losing any significant information. However, if we can so easily characterize the data as if discrete scattering points were responsible, the obvious question is: what physical processes do these scattering points actually represent? We don't complete an answer to this question here, but we do begin an answer with a description of some of their properties and behavior. We present in Section 2 a description of the hardware as designed and in Section 3 a description of its deployment in Puerto Rico, where the radar was tuned to 3.175 MHz and used the Arecibo Heating Facility's transmitters and transmitting antennas. In Section 4 we show the time domain data, in which the E region and several distinct mesospheric regions can be seen. We show the power vs altitude profile, which is typical of medium-frequency returns and describe the phase behavior of the returns, which can be used for tracking discrete targets such as TIDs and meteors. We describe in Section 5 the IDI algorithm, which involves Fourier transforming the several independent data streams and examining (for each pulse series, at each range-gate and at each Fourier frequency) the phases of the 10 complex Fourier voltages. When it is sufficiently accurate to represent the phase variations along the two linear distributions of antennas as linear with distance, we replace the 10 complex voltages with two voltages and two phase gradients. The data are thus cast into a form that is most easily interpreted as the result of scattering from a number of simultaneous discrete points. In Section 6 we describe some of the properties of these scattering points. The polarization properties of the points are shown first, since this is used for filtering the results that follow. We show the distribution of radial velocities with altitude for the ordinary, extraordinary and linear modes. The radial velocities show the characteristic mesospheric-scattering distribution of the ordinary-mode points (which was the transmitted mode), contrasted with the near-random distributions of the linear and extraordinary-mode points. This justifies the use of polarization filtering and introduces a powerful new filtering technique. Next we show the combined power of the scattering points (the ‘recovered’ power) and its variation with altitude and time. The recovered power looks very much like the raw power as usually seen by medium-frequency radars (one to several mesospheric regions plus the E region), except that it has somewhat better altitude resolution (being in altitude rather than range) and better low-altitude coverage due to ≈ 10 dB better signal/noise. Skymaps of the scattering points (i.e. their locations in the horizontal plane) are shown at several altitudes, showing the varying spread and sometimes asymmetry, in their distribution. We then show the variation of the recovered power with zenith angle, demonstrating the aspect sensitivity of the returns, from nearly specular at 60 80 km, spreading out to a maximum around 90 100 km and contracting sharply to very mirror-like above that. The motions of the scattering points are explored with contour maps of horizontal layers and by calculating their three-dimensional mean motions. Estimates of the calcultional uncertainties are made for the locations and motions of the points.

THE GREAT DISMAL SWAMP: MANAGEMENT OF A HYDROLOGIC RESOURCE WITH THE AID OF REMOTE SÉNSING1

ABSTRACT: Both color infrared aerial photography and Landsat data are being used to provide information to meet present and future management goals for the Great Dismal Swamp National Wildlife Refuge. High and low altitude color infrared photographs are being used to study the hydrology and map the present vegetation of the swamp. A variety of significant ecologic units have been identified using these photographs. The completed maps will be used to evaluate analyses of landsat digital data. Once the present data base is compiled, it is hoped that routine analysis of Landsat data can be used for updating or to indicate areas where low altitude coverage or ground checking is desirable. The data base will also aid in identifying and evaluating trends that may provide guidelines for wetland management.