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NASA NTRS2000

Performance Modeling of an Airborne Raman Water Vapor Lidar

A sophisticated Raman lidar numerical model had been developed. The model has been used to simulate the performance of two ground-based Raman water vapor lidar systems. After tuning the model using these ground-based measurements, the model is used to simulate the water vapor measurement capability of an airborne Raman lidar under both day-and night-time conditions for a wide range of water vapor conditions. The results indicate that, under many circumstances, the daytime measurements possess comparable resolution to an existing airborne differential absorption water vapor lidar while the nighttime measurement have higher resolution. In addition, a Raman lidar is capable of measurements not possible using a differential absorption system.

Whiteman, D. N.↗

NASA NTRS1997

Microphysical Retrievals Over Stratiform Rain Using Measurements from an Airborne Dual-Wavelength Radar-Radiometer

The need to understand the complementarity of the radar and radiometer is important not only to the Tropical Rain Measuring Mission (TRMM) program but to a growing number of multi-instrumented airborne experiment that combine single or dual-frequency radars with multichannel radiometers. The method of analysis used in this study begins with the derivation of dual-wavelength radar equations for the estimation of a two-parameter drop size distribution (DSD). Defining a "storm model" as the set of parameters that characterize snow density, cloud water, water vapor, and features of the melting layer, then to each storm model there will usually correspond a set of range-profiled drop size distributions that are approximate solutions of the radar equations. To test these solutions, a radiative transfer model is used to compute the brightness temperatures for the radiometric frequencies of interest. A storm model or class of storm models is considered optimum if it provides the best reproduction of the radar and radiometer measurements. Tests of the method are made for stratiform rain using simulated storm models as well as measured airborne data. Preliminary results show that the best correspondence between the measured and estimated radar profiles usually can be obtained by using a moderate snow density (0.1-0.2 g/cu cm), the Maxwell-Garnett mixing formula for partially melted hydrometeors (water matrix with snow inclusions), and low to moderate values of the integrated cloud liquid water (less than 1 kg/sq m). The storm-model parameters that yield the best reproductions of the measured radar reflectivity factors also provide brightness temperatures at 10 GHz that agree well with the measurements. On the other hand, the correspondence between the measured and modeled values usually worsens in going to the higher frequency channels at 19 and 34 GHz. In searching for possible reasons for the discrepancies, It is found that changes in the DSD parameter Mu, the radar constants, or the path-integrated attenuation can affect the high frequency channels significantly. In particular, parameters that cause only modest increases in the median mass diameter of the snow, and which have a minor effect on the radar returns or the low frequency brightness temperature, can produce a strong cooling of the 34 GHz brightness temperature.

Meneghini, Robert↗

NASA NTRS2000

Comparison of Aerosol Optical Properties and Water Vapor Among Ground and Airborne Lidars and Sun Photometers During TARFOX

We compare aerosol optical thickness (AOT) and precipitable water vapor (PWV) measurements derived from ground and airborne lidars and Sun photometers during TARFOX (Tropospheric Aerosol Radiative Forcing Observational Experiment). Such comparisons are important to verify the consistency between various remote sensing measurements before employing them in any assessment of the impact of aerosols on the global radiation balance. Total scattering ratio and extinction profiles measured by the ground-based NASA/GSFC Scanning Raman Lidar (SRL) system, which operated from Wallops Island, Virginia (37.86 deg N, 75.51 deg W), are compared with those measured by the Lidar Atmospheric Sensing Experiment (LASE) airborne lidar system aboard the NASA ER-2 aircraft. Bias and rms differences indicate that these measurements generally agreed within about 10%. Aerosol extinction profiles and estimates of AOT are derived from both lidar measurements using a value for the aerosol extinction/backscattering ratio S(sub a)=60 sr for the aerosol extinction/backscattering ratio, which was determined from the Raman lidar measurements.

Ferrare, R.↗

NASA NTRS2000

Modeling the Radiative Characteristics of Airborne Mineral Aerosols at Infrared Wavelengths

We explore the importance of the composition of airborne mineral aerosols for assessments of their direct radiative forcing at infrared wavelengths. Our calculations employing theory and data on spectral refractive indices show that the existing variations in refractive places can cause large changes in the major aerosol optical characteristics. Calculations of IR radiative forcings at the top of the atmosphere and IR downward and upward fluxes, based on an one-dimensional radiation transfer code, give a wide range of results for varying optical models of the mineral aerosols. We estimate that for a "low dust loading" scenario the changes in IR downward flux at the surface relative to dust free conditions are in the range from 7 to 14 W/sq m depending upon the mineral aerosol selected. Under "dry tropics" atmospheric conditions the IR forcing at the top of the atmosphere is in the range from 2 to 7 W/sq m. In turn, for a "high dust loading" scenario the calculated changes, relative to dust free conditions, in IR downward flux at the surface vary from 50 to 80 W/sq m , and the IR forcing at the top of the atmosphere varies from 125 W/sq m. Therefore, we conclude that incorporation of regionally and temporally varying dust mineralogical composition into general circulation models could be beneficial for decreasing the currently large uncertainties in the assessment of radiative forcing by the natural and anthropogenic components of the airborne mineral aerosols. Also the use of appropriate mineralogical data is required for remote sensing of the atmospheric aerosols using satellite infrared observations.

Sokolik, Irina N.↗

NASA NTRS2000

Fault Scarp Detection Beneath Dense Vegetation Cover: Airborne Lidar Mapping of the Seattle Fault Zone, Bainbridge Island, Washington State

The emergence of a commercial airborne laser mapping industry is paying major dividends in an assessment of earthquake hazards in the Puget Lowland of Washington State. Geophysical observations and historical seismicity indicate the presence of active upper-crustal faults in the Puget Lowland, placing the major population centers of Seattle and Tacoma at significant risk. However, until recently the surface trace of these faults had never been identified, neither on the ground nor from remote sensing, due to cover by the dense vegetation of the Pacific Northwest temperate rainforests and extremely thick Pleistocene glacial deposits. A pilot lidar mapping project of Bainbridge Island in the Puget Sound, contracted by the Kitsap Public Utility District (KPUD) and conducted by Airborne Laser Mapping in late 1996, spectacularly revealed geomorphic features associated with fault strands within the Seattle fault zone. The features include a previously unrecognized fault scarp, an uplifted marine wave-cut platform, and tilted sedimentary strata. The United States Geologic Survey (USGS) is now conducting trenching studies across the fault scarp to establish ages, displacements, and recurrence intervals of recent earthquakes on this active fault. The success of this pilot study has inspired the formation of a consortium of federal and local organizations to extend this work to a 2350 square kilometer (580,000 acre) region of the Puget Lowland, covering nearly the entire extent (approx. 85 km) of the Seattle fault. The consortium includes NASA, the USGS, and four local groups consisting of KPUD, Kitsap County, the City of Seattle, and the Puget Sound Regional Council (PSRC). The consortium has selected Terrapoint, a commercial lidar mapping vendor, to acquire the data.

Harding, David J.↗

NASA NTRS2000

Using Airborne Laser Altimetry to Detect Topographic Change at Long Valley Caldera California

The topography of the Long Valley caldera, California, was sampled using airborne laser altimetry in 1993, 1995, and 1997 to test the feasibility of using airborne laser altimetry for monitoring deformation of volcanic origin. Results show the laser altimeters are able to resolve subtle topographic features such as a gradual slope and to detect small transient changes in lake elevation. Crossover and repeat pass analyses of laser tracks indicate decimeter-level vertical precision is obtained over flat and low-sloped terrain for altimeter systems performing waveform digitization. Comparisons with complementary, ground-based CPS data at a site close to Bishop airport indicate that the laser and GPS-derived elevations agree to within the error inherent in the measurement and that horizontal locations agree to within the radius of the laser footprint. A comparison of the data at two sites, one where no change and the other where the maximum amount of vertical uplift is expected, indicates approximately 10 cm of relative uplift occurred 1993-1997, in line with predictions from continuous CPS measurements in the region. Extensive terrain mapping flights during the 1995 and 1997 missions demonstrate some of the unique abilities of laser altimetry; the straightforward creation of high resolution, high accuracy digital elevation models of overflown terrain, and the ability to determine ground topography in the presence of significant ground cover such as dense tree canopies. These capabilities make laser altimetry an attractive technique for quantifying topographic change of volcanic origin, especially in forested regions of the world where other remote sensing instruments have difficulty detecting the underlying topography.

Hofton, M. A.↗

NASA NTRS1999

Using Airborne Laser Altimetry to Detect Topographic Change at Long Valley Caldera, California

The topography of the Long Valley caldera, California, was sampled using airborne laser altimetry in 1993, 1995, and 1997 to test the feasibility of using airborne laser altimetry for monitoring deformation of volcanic origin. Results show the laser altimeters are able to resolve subtle topographic features such as a gradual slope and to detect small transient changes in lake elevation. Crossover and repeat pass analyses of laser tracks indicate decimeter-level vertical precision is obtained over flat and low-sloped terrain for altimeter systems performing waveform digitization. Comparisons with complementary, ground-based GPS data at a site close to Bishop airport indicate that the laser and GPS-derived elevations agree to within the error inherent in the measurement and that horizontal locations agree to within the radius of the laser footprint. A comparison of the data at two sites, one where no change and the other where the maximum amount of vertical uplift is expected, indicates approximately 10 cm of relative uplift occurred 1993-1997, in line with predictions from continuous GPS measurements in the region. Extensive terrain mapping flights during the 1995 and 1997 missions demonstrate some of the unique abilities of laser altimetry; the straightforward creation of high resolution, high accuracy digital elevation models of overflown terrain, and the ability to determine ground topography in the presence of significant ground cover such as dense tree canopies. These capabilities make laser altimetry an attractive technique for quantifying topographic change of volcanic origin, especially in forested regions of the world where other remote sensing instruments have difficulty detecting the underlying topography.

Hofton, M. A.↗

NASA NTRS2000

Photon-Counting Multikilohertz Microlaser Altimeters for Airborne and Spaceborne Topographic Measurements

We consider the optimum design of photon-counting microlaser altimeters operating from airborne and spaceborne platforms under both day and night conditions. Extremely compact Q-switched microlaser transmitters produce trains of low energy pulses at multi-kHz rates and can easily generate subnanosecond pulse-widths for precise ranging. To guide the design, we have modeled the solar noise background and developed simple algorithms, based on Post-Detection Poisson Filtering (PDPF), to optimally extract the weak altimeter signal from a high noise background during daytime operations. Practical technology issues, such as detector and/or receiver dead times, have also been considered in the analysis. We describe an airborne prototype, being developed under NASA's instrument Incubator Program, which is designed to operate at a 10 kHz rate from aircraft cruise altitudes up to 12 km with laser pulse energies on the order of a few microjoules. We also analyze a compact and power efficient system designed to operate from Mars orbit at an altitude of 300 km and sample the Martian surface at rates up to 4.3 kHz using a 1 watt laser transmitter and an 18 cm telescope. This yields a Power-Aperture Product of 0.24 W-square meter, corresponding to a value almost 4 times smaller than the Mars Orbiting Laser Altimeter (0. 88W-square meter), yet the sampling rate is roughly 400 times greater (4 kHz vs 10 Hz) Relative to conventional high power laser altimeters, advantages of photon-counting laser altimeters include: (1) a more efficient use of available laser photons providing up to two orders of magnitude greater surface sampling rates for a given laser power-telescope aperture product; (2) a simultaneous two order of magnitude reduction in the volume, cost and weight of the telescope system; (3) the unique ability to spatially resolve the source of the surface return in a photon counting mode through the use of pixellated or imaging detectors; and (4) improved vertical and transverse spatial resolution resulting from both (1) and (3). Furthermore, because of significantly lower laser pulse energies, the microaltimeter is inherently more eyesafe to observers on the ground and less prone to internal optical damage, which can terminate a space mission prematurely.

Degnan, John J.↗

NASA NTRS2000

High Spatial Resolution Airborne Multispectral Thermal Infrared Remote Sensing Data for Analysis of Urban Landscape Characteristics

We have used airborne multispectral thermal infrared (TIR) remote sensing data collected at a high spatial resolution (i.e., 10m) over several cities in the United States to study thermal energy characteristics of the urban landscape. These TIR data provide a unique opportunity to quantify thermal responses from discrete surfaces typical of the urban landscape and to identify both the spatial arrangement and patterns of thermal processes across the city. The information obtained from these data is critical to understanding how urban surfaces drive or force development of the Urban Heat Island (UHI) effect, which exists as a dome of elevated air temperatures that presides over cities in contrast to surrounding non-urbanized areas. The UHI is most pronounced in the summertime where urban surfaces, such as rooftops and pavement, store solar radiation throughout the day, and release this stored energy slowly after sunset creating air temperatures over the city that are in excess of 2-4'C warmer in contrast with non-urban or rural air temperatures. The UHI can also exist as a daytime phenomenon with surface temperatures in downtown areas of cities exceeding 38'C. The implications of the UHI are significant, particularly as an additive source of thermal energy input that exacerbates the overall production of ground level ozone over cities. We have used the Airborne Thermal and Land Applications Sensor (ATLAS), flown onboard a Lear 23 jet aircraft from the NASA Stennis Space Center, to acquire high spatial resolution multispectral TIR data (i.e., 6 bandwidths between 8.2-12.2 (um) over Huntsville, Alabama, Atlanta, Georgia, Baton Rouge, Louisiana, Salt Lake City, Utah, and Sacramento, California. These TIR data have been used to produce maps and other products, showing the spatial distribution of heating and cooling patterns over these cities to better understand how the morphology of the urban landscape affects development of the UHI. In turn, these data have been used by government officials, urban planners, and other decision-makers, to make more informed decisions on how to mitigate the UHI and its subsequent impacts.

Quattrochi, Dale A.↗

NASA NTRS2000

A Compact Airborne System for SO2 and DMS Measurements for Use on Future GTE Missions Aboard the P-3 or DC-8

This project involved the design and construction of a new instrument for airborne measurement of DMS and SO2. The instrument is intended for use on field missions to study the global atmospheric sulfur cycle. The ultimate scientific goal is to provide insight into the mechanisms of atmospheric transport and transformations impacting both natural and anthropogenic sulfur emissions. This report summarizes the progress made to date and the goals for future work on the project. The PI's for this project have recently relocated from the University of Miami to the University of California, Irvine, and a request has been made to transfer remaining funds to UCI. All equipment associated with this project has been transferred to UCI. The instrument design goal was to develop an instrument roughly one quarter the size and weight of currently available airborne instrumentation used for DMS and S02 measurements. Another goal was full automation, to allow unattended operation for the duration of a P-3 or DC-8 flight. The original performance design specifications for the instrument are given.

Saltzman, Eric S.↗

NASA NTRS2000

BOREAS RSS-12 Airborne Tracking Sunphotometer Measurements

The BOREAS RSS-12 team collected both ground and airborne sunphotometer measurements for use in characterizing the aerosol optical properties of the atmosphere during the BOREAS data collection activities. These measurements are to be used to: 1) measure the magnitude and variability of the aerosol optical depth in both time and space; 2) determine the optical properties of the boreal aerosols; and 3) atmospherically correct remotely sensed data acquired during BOREAS. This data set contains airborne tracking sunphotometer data that were acquired from the C-130 aircraft during its flights over the BOREAS study areas. The data cover selected days and times from May to September 1994. The data are stored in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

Hall, Forrest G.↗

NASA NTRS2001

Airborne Sun photometry and Closure Studies in SAFARI-2000 Dry Season Campaign

From August 13 to September 25, the Southern African Regional Science Initiative's (SAFARI 2000) dry-season airborne campaign studied the complex interactions between the region's ecosystems, air pollution, atmospheric circulation, land-atmosphere interactions, and land use change. The field campaign was timed to coincide with the annual winter fire season in Southern Africa. This challenging campaign. which coordinated ground-based measurement teams, multiple research aircraft, and satellite overpasses across nine African nations, was head quartered at the Petersburg International Airport in South Africa's Northern Province. Among many others, unique coordinated observations were made of the evolution of massive, thick haze layers produced by industrial emissions, biomass burning, marine and biogenic sources. The NASA Ames Airborne Tracking 14-channel Sunphotometer (AATS-14) was operated successfully aboard the University of Washington CV-580 during 24 data flights. The AATS-14 instrument measures the transmission of the direct solar beam at 14 discrete wavelengths (3501558 nm) from which we derive spectral aerosol optical depths (AOD), columnar water vapor (CWV) and columnar ozone. Flying at different altitudes over a fixed location allows derivation of layer AOD and CWV. Data taken during feasible vertical profiles allows derivation of aerosol extinction and water vapor density. In the talk, we show comparisons with ground-based AERONET sun/sky photometer results, with ground based MPL-Net lidar data, and with measurements from a lidar aboard the high flying ER-2 aircraft. We will use measurements from the Ames Solar Spectral Flux Radiometer to derive estimates of solar spectral forcing as a function of aerosol thickness. Validations of TOMS and Terra satellite aerosol and water-vapor retrievals will also be discussed.

Schmid, B.↗

NASA NTRS2000

Airborne Sunphotometry of African Dust and Marine Boundary Layer Aerosols in PRIDE

The Puerto Rico Dust Experiment (PRIDE) was conducted during summer 2000 to study the radiative, microphysical and transport properties of Saharan dust in the Caribbean region. During PRIDE, NASA Ames Research Center's six-channel airborne autotracking sunphotometer (AATS-6) was operated aboard a Piper Navajo airplane based at Roosevelt Roads Naval Station on the northeast coast of Puerto Rico. AATS-6 measurements were taken during 21 science flights off the coast of Puerto Rico in the western Caribbean. Data were acquired within and above the Marine Boundary Layer (MBL) and the Saharan Aerosol Layer (SAL) up to 5.5 km altitude tinder a wide range of dust loadings. Aerosol optical depth (AOD) spectra and columnar water vapor (CWV) values have been calculated from the AATS-6 measurements by using sunphotometer calibration data obtained at Mauna Loa Observatory (3A kin ASL) before (May) and after (October) PRIDE. Mid-visible AOD values measured near the surface during PRIDE ranged from 0.07 on the cleanest day to 0.55 on the most turbid day. Values measured above the MBL were as high as 0.35; values above the SAL were as low as 0.01. The fraction of total column AOD due to Saharan dust cannot be determined precisely from AATS-6 AOD data alone due to the uncertainty in the extent of vertical mixing of the dust down through the MBL. However, analyses of ground-based and airborne in-situ aerosol sampling measurements and ground-based aerosol lidar backscatter data should yield accurate characterization of the vertical mixing that will enable calculation of the Saharan dust AOD component from the sunphotometer data. Examples will be presented showing measured AATS-6 AOD spectra, calculated aerosol extinction and water vapor density vertical profiles, and aerosol size distributions retrieved by inversion of the AOD spectra. Near sea-surface AOD spectra acquired by AATS-6 during horizontal flight legs at 30 m ASL are available for validation of AOD derived from coincident satellite sensor (TOMS, MODIS, MISR) measurements. AATS-6 AOD data acquired during numerous aircraft ascents and descents through the MBL and the SAL should permit atmospheric column closure analyses with respect to aerosol optical depth, extinction, and size distribution by comparison with coincident aircraft-based in-situ particle size distribution measurements and ground-based (Cabras Island, Puerto Rico) micropulse lidar aerosol backscatter measurements. The aerosol information derived from the column closure analyses can be used subsequently to calculate radiative flux changes, which can then be compared with coincident spectral flux measurements taken from aboard the aircraft with a solar spectral flux radiometer.

Livingston, John M.↗

NASA NTRS2000

A Compact Ti:Sapphire Laser With its Third Harmonic Generation (THG) for an Airborne Ozone Differential Absorption Lidar (DIAL) Transmitter

A compact and high-pulse-energy Ti:Sapphire laser with its Third Harmonic Generation (THG) has been developed for an airborne ozone differential absorption lidar (DIAL) to study the distributions and concentrations of the ozone throughout the troposphere. The Ti:Sapphire laser, pumped by a frequency-doubled Nd:YAG laser and seeded by a single mode diode laser, is operated either at 867 nm or at 900 nm with a pulse repetition frequency of 20 Hz. High energy laser pulses (more than 110 mJ/pulse) at 867 nm or 900 nm with a desired beam quality have been achieved and utilized to generate its third harmonic at 289nm or 300nm, which are on-line and off-line wavelengths of an airborne ozone DIAL. After being experimentally compared with Beta-Barium Borate (beta - BaB2O4 or BBO) nonlinear crystals, two Lithium Triborate (LBO) crystals (5 x 5 x 20 cu mm) are selected for the Third Harmonic Generation (THG). In this paper, we report the Ti:Sapphire laser at 900 nm and its third harmonic at 300 nm. The desired high ultraviolet (UV) output pulse energy is more than 30 mJ at 300 nm and the energy conversion efficiency from 900 nm to 300 nm is 30%.

Chen, Songsheng↗

NASA NTRS1994

The Next Generation Airborne Observatory: SOFIA

NASA, DARA, and the astronomical community have planned SOFIA (Stratospheric Observatory for Infrared Astronomy) to extend and expand the capabilities of airborne astronomy. Just as the Kuiper Airborne Observatory telescope has three times the aperture of its Learjet predecessor, SOFIA's aperture (2.5 m) will be three times that of the KAO. Thus SOFIA will surpass the angular resolution of the KAO by a factor of three and its per-pixel sensitivity by a factor approximately 10 at wavelengths beyond 10 micrometers. Following the tradition of the KAO and Learjet programs, the user community will provide most of the SOFIA focal plane instruments. Scientists will fly their new instruments as soon as they become operational, assuring immediate application of state-of-the-art technology throughout the anticipated 20 year observatory lifetime. Annual peer review of submitted proposals guarantees a vigorous observing program. Armed by 15-20 different instrument teams, reinforced by an additional approximately 50 guest investigator groups, and flying 160 8-hour sorties per year, SOFIA will be used to attack a very broad range of astronomical problems. To name just a few, observations made from SOFIA will: greatly extend our understanding of the star-formation process, including collapse, accretion, and outflow phenomena; penetrate the obscuring dust of the Milky way to reveal gas motions, the luminosity distribution, and possibly the powerful excitation mechanism at the center of our Galaxy; and probe km-scale structure of planetary atmospheres and ring systems. The Astronomy and Astrophysics Survey (Bahcall) committee ranked SOFIA as the highest priority moderate cost new mission for NASA in the 1990s. SOFIA has been thoroughly studied and is ready to start development. If funding is available in 1996 as currently planned by NASA and DARA Astrophysics Offices, SOFIA could be flying by the end of the decade.

Erickson, E. F.↗

NASA NTRS2001

AESMIR: A New NASA Airborne Microwave Imager

The Airborne Earth Science Microwave Imaging Radiometer (AESMIR) is a versatile new airborne imaging radiometer under development by NASA. The AESMIR design is unique in that it will perform dual-polarized imaging at all AMSR frequency bands (6.9 through 89 GHz) using only one sensor head/scanner package, providing an efficient solution for AMSR-type science applications (snow, soil moisture/land parameters, precip, ocean winds, SST, water vapor, sea ice, etc.). The microwave radiometers themselves will incorporate state-of-the-art receivers, with particular attention given to instrument calibration for the best possible accuracy and sensitivity. The single-package design of AESMIR makes it compatible with high-altitude aircraft platforms such as the NASA ER-2s and the Proteus. The arbitrary 2-axis gimbal can perform conical and cross-track scanning, as well as fixed-beam staring. This compatibility with high-altitude platforms coupled with the flexible scanning configuration, opens up previously unavailable science opportunities for convection/precip/cloud science and co-flying with complementary instruments, as well as providing wider swath coverage for all science applications. By designing AESMIR to be compatible with these high-altitude platforms, we are also compatible with the NASA P-3, the NASA DC-8, and ground-based deployments. Thus AESMIR can provide low-, mid-, and high altitude microwave imaging.

Kim, Edward J.↗

NASA NTRS1995

The FOSTER Project: Teacher Enrichment Through Participation in NASA's Airborne Astronomy Program

NASA's airborne astronomy program offers a unique opportunity for K-12 science teacher enrichment and for NASA to reach out and serve the educational community. Learning from a combination of summer workshops, curriculum supplement materials, training in Internet skills and ultimately flying on NASA's C-141 airborne observatory, the teachers are able to share the excitement of scientific discovery with their students and convey that excitement from first hand experience rather than just from reading about science in a textbook. This year the program has expanded to include teachers from the eleven western states served by NASA Ames Research Center's Educational Programs Office as well as teachers from communities from around the country where the scientist who fly on the observatory reside. Through teacher workshops and inservice presentations, the FOSTER (Flight Opportunities for Science Teacher EnRichment) teachers are sharing the resources and experiences with many hundreds of other teachers. Ultimately, the students are learning first hand about the excitement of science, the scientific method in practice, the team work involved, the relevance of science to their daily lives and the importance of a firm foundation in math and science in today's technologically oriented world.

Koch, David↗

NASA NTRS2002

Airborne Microwave Imaging of River Velocities

The objective of this project was to determine whether airborne microwave remote sensing systems can measure river surface currents with sufficient accuracy to make them prospective instruments with which to monitor river flow from space. The approach was to fly a coherent airborne microwave Doppler radar, developed by APL/UW, on a light airplane along several rivers in western Washington state over an extended period of time. The fundamental quantity obtained by this system to measure river currents is the mean offset of the Doppler spectrum. Since this scatter can be obtained from interferometric synthetic aperture radars (INSARs), which can be flown in space, this project provided a cost effective means for determining the suitability of spaceborne INSAR for measuring river flow.

Plant, William J.↗