R.-R. Li

Science Systems and Applications, Inc., Maryland, United States

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Publications (9)8.01 Total impact

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    ABSTRACT: The design and early results of the Hyperspectral Imager for the Coastal Ocean (HICO) are presented. The performance requirements imposed on the sensor to measure the low signals and to differentiate the optically complex spectra of the coastal ocean are discussed. It is shown the as-built sensor meets or exceeds the design parameters. Further, environmental products from early retrievals of the HICO imagery are presented.
    Hyperspectral Image and Signal Processing: Evolution in Remote Sensing (WHISPERS), 2010 2nd Workshop on; 07/2010
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    ABSTRACT: Aerosol particles in the atmosphere can affect climate directly by interacting with solar and terrestrial radiation and indirectly by their effect on cloud microphysics, albedo, and precipitation. The atmospheric aerosol products have been derived operationally from multi-channel imaging data collected with the MOderate Resolution Imaging SpectroRadiometers (MODIS) on board the NASA Terra and Aqua spacecrafts. Through analysis of several years' MODIS aerosol products (Collection 4), we have found that the aerosol products over land are slightly contaminated by snow and ice during the springtime snow-melting season. We have developed an empirical technique using MODIS channels centered near 0.66, 0.86 and 1.24 gm and a thermal emission channel near 11 gm to mask out these snow-contaminated pixels over land. Improved aerosol retrievals have been obtained.
    01/2006: pages 2236-2238; , ISBN: 9780780395091
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    ABSTRACT: The MODerate resolution Imaging Spectroradiometer (MODIS) aboard both NASA's Terra and Aqua satellites is making near global daily observations of the earth in a wide spectral range. These measurements are used to derive spectral aerosol optical thickness and aerosol size parameters over both land and ocean. The aerosol products available over land include aerosol optical thickness at three visible wavelengths, a measure of the fraction of aerosol optical thickness attributed to the fine mode and several derived parameters including reflected spectral solar flux at top of atmosphere. Over ocean, the aerosol optical thickness is provided in seven wavelengths from 0.47 microns to 2.13 microns. In addition, quantitative aerosol size information includes effective radius of the aerosol and quantitative fraction of optical thickness attributed to the fine mode. Spectral aerosol flux, mass concentration and number of cloud condensation nuclei round out the list of available aerosol products over the ocean. The spectral optical thickness and effective radius of the aerosol over the ocean are validated by comparison with two years of AERONET data gleaned from 133 AERONET stations. 8000 MODIS aerosol retrievals colocated with AERONET measurements confirm that one-standard deviation of MODIS optical thickness retrievals fall within the predicted uncertainty of delta tauapproximately equal to plus or minus 0.03 plus or minus 0.05 tau over ocean and delta tay equal to plus or minus 0.05 plus or minus 0.15 tau over land. 271 MODIS aerosol retrievals co-located with AERONET inversions at island and coastal sites suggest that one-standard deviation of MODIS effective radius retrievals falls within delta r_eff approximately equal to 0.11 microns. The accuracy of the MODIS retrievals suggests that the product can be used to help narrow the uncertainties associated with aerosol radiative forcing of global climate.
    Journal of the Atmospheric Sciences 02/2003; · 2.67 Impact Factor
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    ABSTRACT: The Moderate Resolution Imaging Spectroradiometer (MODIS) sensor, launched on the National Aeronautics and Space Administration Terra satellite at the end of 1999, was designed with 36 spectral channels for a wide array of land, ocean, and atmospheric investigations. MODIS has a unique ability to observe fires, smoke, and burn scars globally. Its main fire detection channels saturate at high brightness temperatures: 500 K at 4 µm and 400 K at 11 µm, which can only be attained in rare circumstances at the 1 km fire detection spatial resolution. Thus, unlike other polar orbiting satellite sensors with similar thermal and spatial resolutions, but much lower saturation temperatures (e.g. Advanced Very High Resolution Radiometer and Along Track Scanning Radiometer), MODIS can distinguish between low intensity ground surface fires and high intensity crown forest fires. Smoke column concentration over land is for the first time being derived from the MODIS solar channels, extending from 0.41 µm to 2.1 µm. The smoke product has been provisionally validated both globally and regionally over southern Africa and central and south America. Burn scars are observed from MODIS even in the presence of smoke, using the 1.2 to 2.1 µm channels. MODIS burned area information is used to estimate pyrogenic emissions. A wide range of these fire and related products and validation are demonstrated for the wild fires that occurred in northwestern USA in Summer 2000. The MODIS rapid response system and direct broadcast capability is being developed to enable users to obtain and generate data in near real-time. It is expected that health and land management organizations will use these systems for monitoring the occurrence of fires and the dispersion of smoke within two to six hours after data acquisition.
    International Journal of Remote Sensing 01/2003; 24(8):1765-1781. · 1.36 Impact Factor
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    ABSTRACT: 1] The MODerate resolution Imaging Spectroradiometer (MODIS) algorithm for determining aerosol characteristics over ocean is performing within expected accuracy. A two-month data set of MODIS retrievals co-located with observations from the AErosol RObotic NETwork (AERONET) ground-based sunphotometer network provides the necessary validation. Spectral radiation measured by MODIS (in the range 550 –2100 nm) is used to retrieve the aerosol optical thickness, effective particle radius and ratio between the submicron and micron size particles. MODIS-retrieved aerosol optical thickness at 660 nm and 870 nm fall within the expected uncertainty, with the ensemble average at 660 nm differing by only 2% from the AERONET observations and having virtually no offset. Roughly seventy percent of MODIS retrievals of aerosol effective radius for optical thickness greater than 0.15 agree with AERONET retrievals to within ±0.10 mm.
    Geophysical Research Letters 06/2002; 29(12-1618). · 3.98 Impact Factor
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    ABSTRACT: The MODerate Resolution Imaging Spectroradiometer (MODIS) instrument aboard the Terra spacecraft has been retrieving aerosol parameters since late February 2000. Initial qualitative checking of the products showed very promising results including matching of land and ocean retrievals at coastlines. Using AERONET ground-based radiometers as our primary validation tool, we have established quantitative validation as well. Our results show that for most aerosol types, the MODIS products fall within the pre-launch estimated uncertainties. Surface reflectance and aerosol model assumptions appear to be sufficiently accurate for the optical thickness retrieval. Dust provides a possible exception, which may be due to non-spherical effects. Over ocean the MODIS products include information on particle size, and these parameters are also validated with AERONET retrievals.
    02/2000;
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    ABSTRACT: Introduction: In September 2007, NRL, in part-nership with multiple institutions, undertook a com-bined airborne multi-sensor remote sensing campaign and in situ validation effort. The experiment, VCR'07, took place at the Virginia Coast Reserve (VCR), a National Science Foundation–funded Long Term Eco-logical Research (LTER) Site on the Eastern Shore of Virginia. The study area comprised an 1880 km 2 region of barrier islands, shallow water lagoons, and main-land marsh systems (Fig. 4). This article describes the results of a subset of experiments conducted during the campaign demonstrating the retrieval of soil bearing strength directly from hyperspectral remote sensing on the VCR barrier islands. Bearing strength, or "traf-ficability," is a key parameter needed by military plan-ners to identify littoral penetration points. The study also developed and tested new methods for retrieval of shallow water bathymetry, another important param-eter needed by amphibious craft during landing. Background: Hyperspectral imaging (HSI) sensors record the reflected solar radiation from land and water and have been used to retrieve important information in a variety of applications including precision land-cover mapping; in-water retrievals such as bathymetry, bottom type, and suspended constituents; retrieval of biophysical and geophysical parameters on land; and detection and determination of man-made structures and objects. HSI sensors are unique in having a large number of narrow, contiguous spectral channels. They have sufficient spectral resolution to identify different surface characteristics based solely on spectral signa-tures, and allow mapping of retrieved quantities with a high degree of precision.