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An overview of the jet stream and its observation by MST radar is presented. The climatology and synoptic and mesoscale structure of jet streams is briefly reviewed. MST radar observations of jet stream winds, and associated waves and turbulence are then considered. The possibility of using a network of ST radars to track jet stream winds in near real time is explored.
The Precipitation Research Group in NASA MSFC’s Earth Science Branch (ST-11) focuses on observations of precipitation (rain, snow, and hail) from a variety of perspectives: ground-based radars, surface gauge networks, airborne instruments, and spaceborne measurements from onboard satellites. Current work includes identifying signatures of hail and strong thunderstorms from spaceborne measurements and assessing those signatures against multiple satellite datasets and ground-based radar observations. The Precipitation Team is also involved in the development and maintenance of NASA’s global-gridded multi-satellite precipitation product (IMERG) and operating and maintaining the GPM Validation Network (VN): a software package that geometrically matches the reference ground-based weather radar observations with GPM satellite observations in 3D. The team is also responsible for the Advanced Microwave Precipitation Radiometer (AMPR) used in airborne field campaign research, which recently was used to collect data on thunderstorms that produce terrestrial gamma-ray flashes (TGFs) in the Airborne Lightning Observatory for FEGS and TGFs (ALOFT) field campaign. While the Precipitation Group largely supports NASA’s Global Precipitation Measurement (GPM) mission and Precipitation Science Team, the team also looks to the future Precipitation Measurement Mission (PMM) and Investigation of Convective Updrafts (INCUS) missions.
In addition to a report of radar observations concerning the Galilean satellites made in the fall of 1976, Doppler results are presented from 1975 and January 1976. The primary objectives of the investigation conducted in 1976 are related to a study of each satellite at widely separated orbital phases and a close examination of the polarization of its scattered energy. The investigation included an observation of Io, Europa, Ganymede, and Callisto with the upgraded Arecibo S-band radar system on 11 nights irregularly distributed from 26 October 1976 to 7 December 1976. Several peculiarities revealed by the radar observations of the three outer Galilean satellites are related to large and possibly time-varying albedos, and the unexpected result that the circular polarization transmitted exceeds unity by a substantial amount.
The major unknown error in radar altimetry is due to waves on the sea surface which cause the mean radar-reflecting surface to be displaced from mean sea level. This is the electromagnetic bias. The primary motivation for the project was to understand the causes of the bias so that the error it produces in radar altimetry could be calculated and removed from altimeter measurements made from space by the Topex/Poseidon altimetric satellite. The goals of the project were: (1) observe radar scatter at vertical incidence using a simple radar on a platform for a wide variety of environmental conditions at the same time wind and wave conditions were measured; (2) calculate electromagnetic bias from the radar observations; (3) investigate the limitations of the present theory describing radar scatter at vertical incidence; (4) compare measured electromagnetic bias with bias calculated from theory using measurements of wind and waves made at the time of the radar measurements; and (5) if possible, extend the theory so bias can be calculated for a wider range of environmental conditions.
The Terminal Doppler Weather Radar (TDWR) testbed system was operated during the months of July to August 1988 in a live operational demonstration providing microburst (and related weather hazard) protection to the Stapleton International Airport in Denver, CO. During this time period, the performance of the detection system was carefully monitored in an effort to determine the reliability of the system. Initial performance analysis indicates that the microburst detection component of TDWR satisfies the basic performance goals of 90 percent probability of detection and 10 percent probability of false alarm. An in-depth study of the system performance, based on analysis of both dual-Doppler radar observations and surface mesonet measurements, is in progress to provide a detailed understanding of the observability of microbursts by the radar, the ability of the algorithms to detect microburst observed by the radar, and the timeliness and accuracy of the microburst alarms provided to operational users.
Frequency spectra of horizontal winds in the troposphere and stratosphere, over a range of periods and frequencies, have been studied by means of two radar profilers, located at Plattenville, Colorado, and Poker Flat, Alaska, to determine if the spectra deviations from a consistent power law behavior can be verified in a statistical sense. At Plattenville, the spectrum of both zonal and meridional winds in the troposphere is found to obey a low-frequency regime at periods longer than a few hours and a high-frequency regime at periods less than 1/2 hour. The energy levels in the high-frequency regime are enhanced over those obtained by extrapolation of the low-frequency regime by a factor of 4. At Poker Flat, a similar pattern is found in the stratosphere, and the magnitude of the enhancement factor is 1.7. It is suggested that the enhanced amplitudes reflect the effects of upward-propagating gravity waves launched by the flow over a rough terrain, and that they influence the dynamics of the large-scale circulation to a great extent.
The scientific aims, theoretical principles, techniques and instrumentation, and future potential of radar observations of solar-system objects are discussed in a general overview. Topics examined include the history of radar technology, echo detectability, the Arecibo and Goldstone radar observatories, echo time delay and Doppler shift, radar waveforms, albedo and polarization ratio, measurement of dynamical properties, and the dispersion of echo power. Consideration is given to angular scattering laws; the radar signatures of the moon and inner planets, Mars, and asteroids; topographic relief; delay-Doppler radar maps and their physical interpretation; and radar observations of the icy Galilean satellites of Jupiter, comets, and the rings of Saturn. Diagrams, drawings, photographs, and sample maps and images are provided.
For the 30 asteroids and 4 comets for which radar astrometric data were given by Ostro (1991), orbits have been computed using both the radar and the existing optical measurements. The techniques required to process radar data in orbit determination solutions are outlined, and future radar observation opportunities for asteroids and comets are identified. For asteroids and comets that have only short intervals of optical astrometric data, the additional use of only a few radar observations allows a far more accurate extrapolation of their future motions. The use of radar data can often ensure an object's successful recovery at future earth returns and greatly assist efforts in monitoring the motions of the rapidly growing population of known near-earth objects, including their future close-earth approaches.
Software to support all stages of asteroid radar observation and data analysis is developed. First-order analysis of all data in hand is complete. Estimates of radar cross sections, circular polarization ratios, and limb-to-limb echo spectral bandwidths for asteroids 7 Iris, 16 Psyche, 97 Klotho, 1862 Apollo, and 1915 Quetzalcoatl are reported. Radar observations of two previously unobserved asteroids were conducted. An Aten asteroid, 2100 Ra-Shalom, with the smallest known semimajor axis (0.83) was detected. Preliminary data reduction indicates a circular polarization ratio comparable to those of Apollo, Quetzalcoatl, and Toro.
Understanding the ion chemistry and conditions leading to the formation of ionospheric depletions (ionospheric holes) was an important objective of the NASA active ionospheric experiment program. Millstone Hill radar observations were used to monitor the magnitude and temporal extent of the plasma holes produced under varying conditions. The major objective of the completed project was to provide radar diagnostic support for individual NASA rocket campaigns flown from Wallops Island. Two rocket programs, NICARE and REDAIR 2, were selected by NASA for radar support during the proposal period and pre-launch and in-flight radar observations were provided for each as well as basic reduction of the acquired data for scientific analysis. Radar operations and analysis for both of these experiments were performed as proposed and the work on these projects at M.I.T. was completed.
Solid rocket motor (SRM) slag has been identified as a significant source of man-made orbital debris. The propensity of SRMs to generate particles of 100 m and larger has caused concern regarding their contribution to the debris environment. Radar observation, rather than in-situ gathered evidence, is currently the only measurable source for the NASA/ODPO model of the on-orbit slag population. This simulated model includes the time evolution of the resultant orbital populations using a historical database of SRM launches, propellant masses, and estimated locations and times of tail-off. However, due to the small amount of observational evidence, there can be no direct comparison to check the validity of this model. Rather than using the assumed population developed from purely historical and physical assumptions, a regressional approach was used which utilized the populations observed by the Haystack radar from 1996 to present. The estimated trajectories from the historical model of slag sources, and the corresponding plausible detections by the Haystack radar, were identified. Comparisons with observational data from the ensuing years were made, and the SRM model was altered with respect to size and mass production of slag particles to reflect the historical data obtained. The result is a model SRM population that fits within the bounds of the observed environment.
Lunar thermal emission theory, and instrumentation for radar observations of moon
Repeat-pass, interferometric, radar observations of tropical rain-forests colected by the Shuttle Imaging Radar SIR-C in Rondonia, Brazil reveal C-band (5.6-cm) radar signals completely decorelate over forest, whereas L-band (24-cm) signals remain strongly coherent over the intire landscape. At L-band, the difference in elevation between forest and clearings is within the 8-m height noise of the data. Atmospheric delays are large, however, forming kilometer-sized anomalies with a with a 1.2-cm rms one way. Radar interferometric studies of humid tropics miust be conducted at long radar wavelengths, with kilometric baselines or with two antennas operating simultaneously.
Since the deployment of the DMSP SSM/I microwave imagers in 1987, increased utilization of passive microwave radiometry throughout the 10 - 100 GHz spectrum has occurred for measurement of atmospheric constituents and terrestrial surfaces. Our efforts have focused on observations and analysis of the microwave radiative transfer behavior of precipitating clouds. We have focused particular attention on combining both aircraft and SSM/I radiometer imagery with ground-based multiparameter radar observations. As part of this and the past NASA contract, we have developed a multi-stream, polarized radiative transfer model which incorporates scattering. The model has the capability to be initialized with cloud model output or multiparameter radar products. This model provides the necessary 'link' between the passive microwave radiometer and active microwave radar observations. This unique arrangement has allowed the brightness temperatures (TB) to be compared against quantities such as rainfall, liquid/ice water paths, and the vertical structure of the cloud. Quantification of the amounts of ice and water in precipitating clouds is required for understanding of the global energy balance.
Global Precipitation Measurement Mission (GPM) retrieval algorithm validation requires datasets that characterize the 4-D structure, variability, and correlation properties of hydrometeor particle size distributions (PSD) and accumulations over satellite fields of view (5 -- 50 km). Key to this process is the combined use of disdrometer and polarimetric radar platforms. Here the disdrometer measurements serve as a reference for up-scaling dual-polarimetric radar observations of the PSD to the much larger volumetric sampling domain of the radar. The PSD observations thus derived provide a much larger data set for assessing DSD variability, and satellite-based precipitation retrieval algorithm assumptions, in all three spatial dimensions for a range of storm types and seasons. As one component of this effort, the GPM Ground Validation program recently acquired five 3rd generation 2D Video disdrometers as part of its Disdrometer and Radar Observations of Precipitation Facility (DROP), currently hosted in northern Alabama by the NASA Marshall Space Flight Center and the University of Alabama in Huntsville. These next-generation 2DVDs were operated and evaluated in different phases of data collection under the scanning domain of the UAH ARMOR C-band dual-polarimetric radar. During this period approximately 7500 minutes of PSD data were collected and processed to create gamma size distribution parameters using a truncated method of moments approach. After creating the gamma parameter datasets the DSDs were then used as input to T-matrix code for computation of polarimetric radar moments at C-band. The combined dataset was then analyzed with two basic objectives in mind: 1) the investigation of seasonal variability in the rain PSD parameters as observed by the 2DVDs; 2) the use of combined polarimetric moments and observed gamma distribution parameters in a functional form to retrieve PSD parameters in 4-D using the ARMOR radar for precipitation occurring in different seasons and for different rain system types. Preliminary results suggest that seasonal variations in the DSD parameters do occur, but are most pronounced when comparing tropical PSDs to either winter or summer convective precipitation. For example the previously documented shift to relatively smaller drop diameters in higher number concentrations for equivalent rain rate bins was observed in tropical storm rainbands occurring over Huntsville. On a more inter seasonal basis empirical fits between parameters such as D0 and ZDR do not appear to exhibit robust seasonal biases- i.e., one fit seems to work for all seasons within acceptable standard error (O[10%]) for estimates of D0. In polarimetric retrievals of the vertical variability in PSD (rain layer) for a tropical rainband we find that the Do varies with height when partitioned by specified precipitation categories (e.g., convective or stratiform, heavy and light stratiform etc.) but this variation is of order 10-20% and is smaller than the difference in D0 observed between the basic delineation of convective and stratiform precipitation types. Currently we are expanding our analysis of the vertical structure of the PSD to include several seasonally and/or dynamically-different storm system types (e.g., winter convection and stratiform events; summer mid-latitude convective etc.) sampled by ARMOR. The study will present the results of our combined analyses.
Strategic roadmaps for NASA's Human Exploration and Development of Space (REDS) enterprise support near-term high-frequency communication systems that provide moderate to high data rates with dependable service. Near-earth and human planetary exploration will baseline Ka-Band, but may ultimately require the use of even higher frequencies. Increased commercial demand on low-frequency earth-space bands has also led to increased interest in the use of higher frequencies in regions like K u - and K,- band. Data is taken from the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR), which operates at 13.8 GHz, and the true radar reflectivity profile is determined along the PR beam via low-frequency ground based polarimetric observations. The specific differential phase (Kdp) is measured along the beam and a theoretical model is used to determine the expected specific attenuation (k). This technique, called the k-Kdp method, uses a Fuzzy-Logic model to determine the hydrometeor type along the PR beam from which the appropriate k-Kdp relationship is used to determine k and, ultimately, the total path-integrated attenuation (PIA) on PR measurements. Measurements from PR and the NCAR S-POL radar were made during the TEFLUN-B experiment that took place near Melbourne, FL in 1998, and the TRMM-LBA campaign near Ji-Parana, Brazil in 1999.
High-resolution Viking Orbiter images contain significant information on Martian surface roughness at 25- to 100-m lateral scales, while earth-based radar observations of Mars are sensitive to roughness at lateral scales of 1 to 30 m or more. High-rms slopes predicted for the Tharsis-Memnonia-Amazonis volcanic plains from extremely weak radar returns are qualitatively confirmed by the Viking image data. Large-scale, curvilinear ridges on lava flows in the Memnonia Fossae region are interpreted as innate flow morphology caused by compressional foldover of moving lava sheets of possible rhyolite-dacite composition. The presence or absence of a recent mantle of fine-grained eolian material on the volcanic surfaces studied was determined by the visibility of fresh impact craters with diameters less than 50 m. Lava flows with surfaces modified by eolian erosion and deposition occur west-northwest of Apollinaris Patera at the border of the cratered equatorial uplands and southern Elysium Planitia. Nearby yardangs, for which radar observations indicate very high-rms slopes, are similar to terrestrial features of similar origin.
Accurate targeting of the Deep Space Program Science Experiment (DSPSE) spacecraft to achieve a 100 km sunward flyby of asteroid 1620 Geographos will require that the ground-based ephemeris of Geographos be well known in advance of the encounter. Efforts are underway to ensure that precision optical and radar observations are available for the final asteroid orbit update that takes place several hours prior to the DSPSE flyby. Because the asteroid passes very close to the Earth six days prior to the DSPSE encounter, precision ground-based optical and radar observations should be available. These ground-based data could reduce the asteroid's position uncertainties (1-sigma) to about 10 km. This ground-based target ephemeris error estimate is far lower than for any previous comet or asteroid that has been under consideration as a mission target.