KEYWORDS: Polarization, Polarimetry, Clouds, Radiometry, Soil science, Signal to noise ratio, Mass attenuation coefficient, Antennas, Microwave radiation, Nose
Polarimetric signatures of terrain features and man-made objects have been measured using unique Direct Detection
Polarimetric Radiometers (DDPR). The DDPRs are lightweight inexpensive systems operating at 35 and 94 GHz. Each
system consists of a single antenna, amplifier, and a truncated cylindrical waveguide that directly measures Q, U, and V.
The highly portable DDPRs are ideal for obtaining the Stokes vectors needed to study the physical characteristics of
natural and man-made features. Field evaluations using the DDPR systems include measurements from an airborne
platform over different terrain features and water, and ground based measurements of the polarimetric signature of grass,
asphalt, buildings, and concealed munitions. The DDPR can function as a bistatic system by using an active source of
polarization. Using this configuration and a soil chamber, we have investigated the effect of soil type and soil moisture
on linear and circular polarization. This report will describe the DDPR and present the analysis of the airborne and
ground based measurements, including the effects of soil type and soil moisture on sources of linear and circular
polarization.
The multi-agency Flight in Icing Remote Sensing Team (FIRST), a consortium of the National Aeronautics and
Space Administration (NASA), the Federal Aviation Administration (FAA), the National Center for Atmospheric
Research (NCAR), the National Oceanographic and Atmospheric Administration (NOAA), and the Army Corps of
Engineers (USACE), has developed technologies for remotely detecting hazardous inflight icing conditions. The
USACE Cold Regions Research and Engineering Laboratory (CRREL) assessed the potential of onboard passive
microwave radiometers for remotely detecting icing conditions ahead of aircraft. The dual wavelength system
differences the brightness temperature of Space and clouds, with greater differences potentially indicating closer and
higher magnitude Cloud Liquid Water Content (CLWC). The Air Force RADiative TRANsfer model (RADTRAN)
was enhanced to assess the flight track sensing concept, and a "flying" RADTRAN was developed to simulate a
radiometer system flying through simulated clouds. Neural network techniques were developed to invert brightness
temperatures and obtain integrated cloud liquid water. In addition, a dual wavelength Direct-Detection Polarimeter
Radiometer (DDPR) system was built for detecting hazardous drizzle drops. This paper reviews technology
development to date and addresses initial polarimeter performance.
NASA has teamed with the FAA, DoD, industry, and academia for research into the remote detection and measurement
of atmospheric conditions leading to aircraft icing hazards. The ultimate goal of this effort is to provide pilots,
controllers, and dispatchers sufficient information to allow aircraft to avoid or minimize their exposure to the hazards of
in-flight icing. Since the hazard of in-flight icing is the outcome of aircraft flight through clouds containing supercooled
liquid water and strongly influenced by the aircraft's speed and configuration and by the length of exposure, the hazard
can't be directly detected, but must be inferred based upon the measurement of conducive atmospheric conditions.
Therefore, icing hazard detection is accomplished through the detection and measurement of liquid water in regions of
measured sub-freezing air temperatures. The icing environment is currently remotely measured from the ground with a
system fusing radar, lidar, and multi-frequency microwave radiometer sensors. Based upon expected ice accretion
severity for the measured environment, a resultant aircraft hazard is then calculated. Because of the power, size, weight,
and view angle constraints of airborne platforms, the current ground-based solution is not applicable for flight. Two
current airborne concepts are the use of either multi-frequency radiometers or multi-frequency radar. Both ground-based
and airborne solutions are required for the future since ground-based systems can provide hazard detection for all aircraft
in airport terminal regions while airborne systems will be needed to provide equipped aircraft with flight path coverage
between terminal regions.
We describe the concept for a logic-tree based geographic information system (GIS) that can infer subsurface geology
and material properties using geoinformatics concepts. A proof-of-concept system was devised and tested integrating the
capabilities of traditional terrain- and image-analysis procedures with a GIS to manipulate geospatial data. Structured
logic trees were developed to guide an analyst through an interactive, geologic analysis based on querying and
mentoring heuristic logic. The hypotheses were that a GIS can be programmed to 1) follow the fundamental logic
sequence developed for traditional terrain- and image analysis procedures; 2) augment that sequence with correlative
geospatial data from a variety of sources; and 3) integrate the inferences and data to develop "best-guess" estimates. We
also developed a method to estimate depth to bedrock, and expanded an existing method to determine water table depth.
Blind evaluations indicate that an analyst can infer the correct geologic conditions 70-80% of the time using this method.
This geologic analysis technique can be applied wherever an estimate of subsurface geology is needed. We apply the
results of our geological analysis to the prediction of local site specific seismic propagation. Comparisons are made with
synthetic seismograms computed from a limited set of geological vignettes.
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