Simone Tanelli

CloudSat's Cloud Profiling Radar After Two Years in Orbit: Performance, Calibration, and Processing

The Cloud Profiling Radar, the sole science instrument of the CloudSat Mission, is a 94-GHz nadir-looking radar that measures the power backscattered by hydrometeors (clouds and precipitation) as a function of distance from the radar. This instrument has been acquiring global time series of vertical cloud structures since June 2, 2006. In this paper, an overview of the radar performance and status, to date, is provided together with a description of the basic data products and the surface clutter rejection algorithm introduced for the Release 04 data product release.

NASA's Genesis and Rapid Intensification Processes (GRIP) Field Experiment

In August–September 2010, NASA, NOAA, and the National Science Foundation (NSF) conducted separate but closely coordinated hurricane field campaigns, bringing to bear a combined seven aircraft with both new and mature observing technologies. NASAs Genesis and Rapid Intensification Processes (GRIP) experiment, the subject of this article, along with NOAAs Intensity Forecasting Experiment (IFEX) and NSFs Pre-Depression Investigation of Cloud-Systems in the Tropics (PREDICT) experiment, obtained unprecedented observations of the formation and intensification of tropical cyclones. The major goal of GRIP was to better understand the physical processes that control hurricane formation and intensity change, specifically the relative roles of environmental and inner-core processes. A key focus of GRIP was the application of new technologies to address this important scientific goal, including the first ever use of the unmanned Global Hawk aircraft for hurricane science operations. NASA and NOAA conducted coord...

Simultaneous measurements of ku- and ka-band sea surface cross sections by an airborne Radar

The dual-frequency Airborne Precipitation Radar-2 (APR-2) was deployed during the Wakasa Bay Experiment in 2003, for validation of the Advanced Microwave Scanning Radiometer-EOS. Besides providing extensive observations of diverse precipitating systems, this Ku-(13.4 GHz) and Ka-band (35.6 GHz) cross-track scanning radar measured sea surface backscatter simultaneously. While the characteristics of the normalized sea surface cross section sigma0 at Ku-band are well understood and widely published, the existing experimental data concerning sigma0 at Ka-band are scarce and results are inconsistent. In this letter, the Ku/Ka-band sigma0 measurements collected by APR-2, together with the estimated uncertainties, are discussed. In general, the measured sigma0 at Ka-band at around 10deg incidence angle appears to be close to that at Ku-band sigma0, and Ka-band exhibits a nonnegligible difference in wind dependence with respect to Ku-band for moderate to high winds

Microwave tomographic inversion technique based on stochastic approach for rainfall fields monitoring

The microwave tomographic inversion technique (MTIT) proposed in 1991 for reconstruction of rainfall fields at ground through microwave attenuation measurements is reconsidered. A new algorithm for data inversion is presented [referred to as stochastic reconstruction technique (SRT)] that generally performs better than the one originally adopted [referred to as arithmetic reconstruction technique (ART)]. Improvement is achieved in spatial definition and general reliability of rainfall field reconstruction. The new model adopted to represent the reconstructed rainfall fields leads to a completely different strategy for the inversion problem, and this strategy is based on a global optimization stochastic technique (GOST). Results obtained through the SRT-MTIT are presented in the paper and compared to those obtained by employing the ART-MTIT. It also is shown that, based on the SRT-MTIT approach, fast and reliable time tracking of rainfall events is made possible by exploiting previous reconstructions and by the improved long-term physical consistency of the model adopted for rainfall field decomposition.

The Effects of Nonuniform Beam Filling on Vertical Rainfall Velocity Measurements with a Spaceborne Doppler Radar

Abstract Information on the global distribution of vertical velocity of precipitating particles is needed in estimating latent heat fluxes, and therefore in the general study of energy transportation phenomena in the atmosphere. Such information is not currently available, but it can potentially be obtained by a spaceborne Doppler precipitation radar. In this paper, the expected performance for this type of Doppler radar for measuring vertical rainfall velocity is investigated. Although the high relative speed of the instrument with respect to the rainfall droplets contributes significantly to the spreading of the Doppler spectrum, accurate estimates of the average vertical velocity can be obtained when the rainfall intensity does not vary significantly within the resolution volume of the instrument. Such a result can be inferred through theoretical calculations and is confirmed by analyzing the Doppler spectra simulated using data gathered by the NASA/Jet Propulsion Laboratory (JPL) airborne rain radar i...

Describing the Shape of Raindrop Size Distributions Using Uncorrelated Raindrop Mass Spectrum Parameters

AbstractRainfall retrieval algorithms often assume a gamma-shaped raindrop size distribution (DSD) with three mathematical parameters Nw, Dm, and μ. If only two independent measurements are available, as with the dual-frequency precipitation radar on the Global Precipitation Measurement (GPM) mission core satellite, then retrieval algorithms are underconstrained and require assumptions about DSD parameters. To reduce the number of free parameters, algorithms can assume that μ is either a constant or a function of Dm. Previous studies have suggested μ–Λ constraints [where Λ = (4 + μ)/Dm], but controversies exist over whether μ–Λ constraints result from physical processes or mathematical artifacts due to high correlations between gamma DSD parameters. This study avoids mathematical artifacts by developing joint probability distribution functions (joint PDFs) of statistically independent DSD attributes derived from the raindrop mass spectrum. These joint PDFs are then mapped into gamma-shaped DSD parameter j...

Triple-Frequency Radar Reflectivity Signatures of Snow: Observations and Comparisons with Theoretical Ice Particle Scattering Models

AbstractAn observation-based study is presented that utilizes aircraft data from the 2003 Wakasa Bay Advanced Microwave Scanning Radiometer Precipitation Validation Campaign to assess recent advances in the modeling of microwave scattering properties of nonspherical ice particles in the atmosphere. Previous work has suggested that a triple-frequency (Ku–Ka–W band) reflectivity framework appears capable of identifying key microphysical properties of snow, potentially providing much-needed constraints on significant sources of uncertainty in current snowfall retrieval algorithms used for microwave remote sensing instruments. However, these results were based solely on a modeling framework. In contrast, this study considers the triple-frequency approach from an observational perspective using airborne radar observations from the Wakasa Bay field campaign. After accounting for several challenges with the observational dataset, such as beam mismatching and attenuation, observed dual-wavelength ratio results ar...

Understanding the relationships between lightning, cloud microphysics, and airborne radar-derived storm structure during Hurricane Karl (2010)

This study explores relationships between lightning, cloud microphysics, and tropical cyclone (TC) storm structure in Hurricane Karl (16 September 2010) using data collected by the NASA DC-8 and Global Hawk (GH) aircraft during NASA’s Genesis and Rapid Intensification Processes (GRIP) experiment. The research capitalizes on the unique opportunity provided by GRIP to synthesize multiple datasets from two aircraft and analyze the microphysical and kinematic properties of an electrified TC. Five coordinated flight legs through Karl by the DC-8 and GH are investigated, focusing on the inner-core region (within 50km of the storm center) where the lightning was concentrated and the aircraft were well coordinated. GRIP datasets are used to compare properties of electrified and nonelectrified inner-core regions that are related to the noninductive charging mechanism, which is widely accepted to explain the observed electric fields within thunderstorms. Three common characteristics of Karl’s electrified regions are identified: 1) strong updrafts of 10‐20ms 21 , 2) deep mixed-phase layers indicated by reflectivities .30dBZ extending several kilometers above the freezing level, and 3) microphysical environments consisting of graupel, very small ice particles, and the inferred presence of supercooled water. These characteristics describe an environment favorable for in situ noninductive charging and, hence, TC electrification. The electrified regions in Karl’s inner core are attributable to a microphysical environment that was conducive to electrification because of occasional, strong convective updrafts in the eyewall.

Rainfall Doppler Velocity Measurements from Spaceborne Radar: Overcoming Nonuniform Beam-Filling Effects

Abstract For vertical Doppler velocity measurements of a homogeneous rain field, the standard spectral moment estimation techniques commonly used by ground-based and airborne Doppler rain radars can be readily extended for spaceborne application, provided that the radar antenna size is chosen to adequately reduce the satellite motion-induced Doppler spectral broadening. When encountering an inhomogeneous rain field, on the other hand, the nonuniform beam filling (NUBF) causes additional biases on Doppler velocity estimates, which (i) often reach several meters per second, (ii) cannot be corrected with standard spectral moment techniques, and (iii) are strongly dependent on the along-track reflectivity profile within the radar footprint. One approach to overcome this difficulty is to further increase the antenna size such that the radars horizontal resolution would be sufficiently small to resolve the inhomogeneity in rain cells. Unfortunately, this approach is very challenging in terms of antenna technol...

Global Precipitation Measurement Cold Season Precipitation Experiment (GCPEx): For Measurement Sake Let it Snow

AbstractAs a component of Earth’s hydrologic cycle, and especially at higher latitudes, falling snow creates snowpack accumulation that in turn provides a large proportion of the freshwater resources required by many communities throughout the world. To assess the relationships between remotely sensed snow measurements with in situ measurements, a winter field project, termed the Global Precipitation Measurement (GPM) Cold Season Precipitation Experiment (GCPEx), was carried out in the winter of 2011/12 in Ontario, Canada. Its goal was to provide information on the precipitation microphysics and processes associated with cold season precipitation to support GPM snowfall retrieval algorithms that make use of a dual-frequency precipitation radar and a passive microwave imager on board the GPM core satellite and radiometers on constellation member satellites. Multiparameter methods are required to be able to relate changes in the microphysical character of the snow to measureable parameters from which precip...