IEEE Geoscience and Remote Sensing Letters

Published by Institute of Electrical and Electronics Engineers
Online ISSN: 1545-598X
Publications
Article
Modeling electromagnetic wave propagation in rain requires knowledge of the complex permittivity of rainwater. In response, we measured the complex permittivity of rainwater in the 0.5-26.5 GHz frequency range using an Agilent Technologies 85070E Dielectric Probe Kit and an Agilent N5242A-400 Vector Network Analyzer. Rainwater samples were collected in Graz (Austria) and Kototabang (Indonesia). The results obtained were found to differ slightly from those of Ray's and Liebe's models. However, the difference in the complex permittivity of rainwater between the measurement and model results exhibits very small biases in the Mie extinction coefficients ( <; 0.01%).
 
Block diagram of the exploited SBAS-DInSAR processing chain.
Computed DInSAR data. (a) Representation of the generated interferograms with respect to the temporal (upper) and perpendicular (lower) baseline amplitudes. (b) SAR data distribution in the plane relevant to the interferogram perpendicular baselines and acquisition dates, the latter represented with " ddmmyyyy. "  
SBAS-DInSAR results. (a) Mean deformation velocity map (in color) superimposed on a SRTM DEM (gray scale) of the zone; the locations of the 2799 and 2853 frames have been highlighted as well as the DInSAR reference point (white square). (b) through (f) DInSAR deformation time series for the pixels marked by triangles in Fig. 3(a) and labeled by the letters from B to F. The study area location is shown in the inset (upper right-hand corner).
SBAS-DInSAR results cross-comparison. (a) Mean deformation velocity map for the 2799 frame data processed via conventional SBAS algorithm. (b) Difference between the deformation velocity map shown in Fig. 4(a) and the one relevant to the corresponding area in Fig. 3(a); the black arrows indicate the locations of the main discrepancies between the two measurements. (c) Standard deviation of the difference between the homologous deformation time series.  
Article
We present the results of the first experiment to survey the temporal evolution of the deformation affecting very large areas using the small baseline subset (SBAS) differential synthetic aperture radar interferometry (DInSAR) algorithm. In particular, we have analyzed a set of 264 descending European Remote Sensing (ERS) SAR data frames from 1992 to 2000; these data are relevant to an area in central Nevada (U.S.) that extends for about 600times100 km. The starting point of our study has been the generation of an appropriate set of small baseline multilook interferograms computed from long SAR image strips, which were obtained by jointly focusing six contiguous raw data frames. Following their generation, the selected interferograms, which are computed on a spatial grid of 160times160 m, have been inverted via the SBAS technique to retrieve, for each coherent pixel, the displacement time series and the corresponding mean deformation velocity. The presented results are, to our knowledge, the first ones with such an extended multitemporal SAR data set, and they demonstrate the effectiveness of the approach to analyze the deformation of the investigated zone.
 
Scatterplot of the optimized roughness (h) versus the modeled roughness according to (4).
Evaluation of LPRM soil-moisture ( sm ) retrieval with ground observations. Red symbols are sites classified as crops, while black symbols are sites classified as grassland. Note that no significant deviation is found between different vegetation types. 
Article
The Land Parameter Retrieval Model (LPRM) has been successfully applied to retrieve soil moisture from space-borne passive microwave observations at C-, X-, or Ku-band and high incidence angles (50deg-55<sup>deg</sup>). However, LPRM had never been applied to lower angles or to L-band observations. This letter describes the parameterization and performance of LPRM using aircraft and ground data from the National Airborne Field Experiment 2005. This experiment was undertaken in November 2005 in the Goulburn River catchment, which is located in southeastern Australia. It was found that model convergence could only be achieved with a temporally dynamic roughness. The roughness was parameterized according to incidence angle and soil moisture. These findings were integrated in LPRM, resulting in one uniform parameterization for all sites. The parameterized LPRM correlated well with field observations at 5-cm depth ( r = 0.93 based on all sites) with a negligible bias and an accuracy of 0.06 m<sup>3</sup>middotm<sup>-3</sup>. These results demonstrate comparable retrieval accuracies as the official SMOS soil-moisture retrieval algorithm (L-MEB), but without the need for the ancillary data that are required by L-MEB. However, care should be taken when using the proposed dynamic roughness model as it is based on a limited data set, and a more thorough evaluation is necessary to test the validity of this new approach to a wider range of conditions.
 
(Left) Ground-based measurement of VWC versus LAI for each vegetation type in the study area, and (right) time series of MODIS eight-day LAI product extracted for each 1-km pixel. 
Article
The spatial and temporal invariance of Soil Moisture and Ocean Salinity (SMOS) forward model parameters for soil moisture retrieval was assessed at 1-km resolution on a diurnal basis with data from the National Airborne Field Experiment 2006. The approach used was to apply the SMOS default parameters uniformly over 27 1-km validation pixels, retrieve soil moisture from the airborne observations, and then to interpret the differences between airborne and ground estimates in terms of land use, parameter variability, and sensing depth. For pastures (17 pixels) and nonirrigated crops (5 pixels), the root mean square error (rmse) was 0.03 volumetric (vol./vol.) soil moisture with a bias of 0.004 vol./vol. For pixels dominated by irrigated crops (5 pixels), the rmse was 0.10 vol./vol., and the bias was -0.09 vol./vol. The correlation coefficient between bias in irrigated areas and the 1-km field soil moisture variability was found to be 0.73, which suggests either 1) an increase of the soil dielectric roughness (up to about one) associated with small-scale heterogeneity of soil moisture or/and 2) a difference in sensing depth between an L-band radiometer and the in situ measurements, combined with a strong vertical gradient of soil moisture in the top 6 cm of the soil.
 
Time series of (black) TIR ground observations, (blue) MW observations, and (red) downscaled MODIS observations 20 km × 20 km. Gray areas indicate periods with clouds; black areas indicate hours with rainfall. 
Article
Two different remotely sensed land surface temperature ( T <sub>s</sub>) products are compared with in situ observations from the National Airborne Field Experiment research site in the western part of the Murrumbidgee catchment, Australia. The remotely sensed T <sub>s</sub> products are retrieved from the following: 1) Ka-band passive microwave (MW) observations using several of space-based MW radiometers and 2) thermal infrared observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) on two satellite platforms. Both methods show similar accuracy when compared to ground observations, although the dynamic range and mean differ significantly. However, a direct comparison of the two products at the same overpass time reveals a strikingly constant relation, with a standard error of ~ 4 K. The results of this study indicate that a merged T <sub>s</sub> product of both MODIS and MW observations is feasible and would decrease the amount of data gaps and increase the sampling frequency for this region to 12 observations a day.
 
Article
In article ldquoOn Huynen's decomposition of a Kennaugh matrixrdquo, equation (6b) is wrong. The correct expression is given in this paper.
 
Article
Soil electromagnetic properties at the microwave frequencies have been extensively documented in the literature. However, similar information at the higher millimeter frequencies is not available. A laboratory experiment was conducted to investigate the extinction behavior of wet and dry soil at millimeter wavelengths (26.5-110 GHz). For dry soil, the extinction coefficient increased from 0.02 to 0.6 cm<sup>-1</sup> as the frequency increased from 26.5 to 110 GHz. The presence of even a small amount of water in the soil (5% by weight) reduced the penetration of millimeter wave signals into soil by a factor of ten.
 
Article
A pitch over maneuver was performed on NOAA-14 to evaluate the Microwave Sounding Unit for asymmetry. This letter presents the results of this test and attempts to explain the asymmetry that the test revealed.
 
Total water content transect used in this study from the GCE cloud model data at simulation time step t = 240 min.  
(a) Brightness temperatures at 89–190 GHz simulated with the RTM. (b) Column-integrated cloud liquid water, rain water, cloud ice, snow, graupel, and water vapor for the transect in Fig. 1.  
Estimation of the canting angle of the tilted structure cloud. The horizontal lines are the altitudes of peaks of the weighting function at (dotted one) 183.3 6 1 GHz and (solid one) 183.3 6 7 GHz, which are taken from the values from Burns et al. [2, Fig. 6(B)]. The vertical lines are the locations of the largest brightness temperature depressions at (dotted one) 183.3 6 1 GHz and (solid one) 183.3 6 7 GHz. The tilted black line passing through the two points of intersection indicates the canting angle of the tilted structure cloud. The arrow in the titled black line shows the direction of the tilted structure cloud. The gray contour is the distribution of total water content for the tilted structure cloud.  
Time series of MIR and EDOP data along the flight track from 1632:05 to 1643:11 UTC on August 26, 1998 during CAMEX-3 (1 min 13 km). (a) Microwave brightness temperatures at the three water vapor channels around 183.3 GHz observed from MIR. (b) EDOP reflectivity cross sections. The tilted black line indicates the canting angle of the tilted structure cloud. The arrow in the black line shows the direction of the tilted structure cloud. The horizontal dotted and solid lines are the altitudes of peaks of the weighting function at 183.3 6 1 and 183.3 6 7 GHz, respectively. The vertical dotted and solid lines are the locations of the largest brightness temperature depressions at 183.3 6 1 and 183.3 6 7 GHz, respectively.  
Article
The effects of cloud structures on microwave radiances at frequencies from 89-190 GHz are investigated by simulations using the Goddard cumulus ensemble model data as input for a radiative transfer model. It was found that the brightness temperatures at these frequencies have different sensitivities to clouds with a tilted structure. The different sensitivities to altitude and amount of hydrometeors allow the estimation of the canting angle and tilt direction of tilted clouds using brightness temperatures at the water vapor channels at 183.3 ± 1 and 183.3 ± 7 GHz. The estimated canting angle and tilt direction are in agreement with the model situation. This method provides a potential to estimate tilted convective structures from microwave radiometric observations at 183.3 ± 1 and 183.3 ± 7 GHz. It is applied to a tilted storm observed from the National Aeronautics and Space Administration's ER-2 aircraft flying at about 20 km on August 26, 1998 during the third Convection and Moisture Experiment using the observed downlooking brightness temperatures at the water vapor channels of a Millimeter-wave Imaging Radiometer. The estimated results are in good agreement with the realistic storm situation obtained from the simultaneous observations of the ER-2 Doppler radar. This method also provides information about the vertical displacement of cloud structure and thereby to estimate the accurate location of surface rainfall. This is important when validating precipitation retrieval based on observations of the ice scattering above surface rainfall against surface rain observations using the microwave frequencies sensitive to high altitudes.
 
Time series (animation) of monthly images of Arctic sea ice age. Week number and year are shown in each image. The animation is available on the IEEE Xplore web page for this letter (http://ieeexplore.ieee.org).
Estimated percent of first-year ice in a 200 2 200 km box centered on the SHEBA field site.
Article
Combining gridded ice motions with daily ice extent maps, it is possible to "track" the evolution of sea ice in the Arctic region. Classifying the ice by ice age, this evolution reveals that the area of the oldest (>4 years) ice is decreasing in the Arctic Basin and is being replaced by younger, first-year ice. As a result, the extent of the oldest ice retreats to a relatively small area north of the Canadian Archipelago, with narrow bands that spread out across the central Arctic. This new approach reinforces the work done by others showing the changes in the Arctic sea ice cover over the past two decades.
 
Map of the region of interest; light (medium) gray is the PSSM application area (area shown in Fig. 3). Lines "S" (St. Anna Trough) and "V" (Voronin Trough) denote gates at 70 • E and 80 • N for Fig. 5. The insert in the upper left is the polynya distribution for March 14, 2003, 5 UTC; white, bright, and dark gray (online: blue) denotes thick ice, thin ice, and open water, respectively. Dimension (grid-cell size) of the map is 2000 km × 1350 km (5 km × 5 km).
(a) Average (1979-2003) daily percentage fraction of given ICCs for the Kara Sea. (b)-(d) Scatterplots of the daily total sea ice area occupied by ICCs 65%-85%, 85%-95%, and > 95% (b), (c), and (d) versus the average daily total polynya area in the Kara Sea for January-April 1996-2003. Areas are normalized with the respective maximum value. Solid lines denote a linear regression with the associated linear correlation coefficient and rms error given in each figure.
Article
The polynya signature simulation method is applied to satellite microwave radiometry data to get the mean (January-April) polynya distribution in the Kara Sea for 1995-2004. Temporal variability of polynya location and extent is confirmed with the variability of ERA40 surface wind speeds. The mean (January-April) fraction of ice area of 65%-85% ice concentration relative to the mean daily total Kara Sea ice area agrees well (correlation coefficient: 0.79) with the mean daily total Kara Sea polynya area for 1996-2003. The resulting linear fit is used to extend the polynya area time series until 1979. During 1979-2003, the polynya area increased by 2400 km<sup>2</sup>/dec. This is accompanied with slightly increasing southerly winds. Polynyas in the eastern Kara Sea seem to play a nonnegligible role for the winter-time Kara Sea ice export.
 
Observed linear relation between ETM+ band 7 (2.09–2.35 m) and band 1 (0.45–52 m) for local regions near 21 AERONET sites, supporting the Kaufmann et al. [13] approach for aerosol extraction. Atmospheric correction for these targets was performed using 6S radiative transfer model, and aerosol optical thickness derived from simultaneous AERONET observations.  
Example of LEDAPS atmospheric correction. (a) Top-of-atmosphere (TOA) reflectance composite (bands 3,2,1) for Landsat-7 ETM+ image of San Francisco Bay (July 7, 1999); (b) Surface reflectance composite.  
Histograms of TOA reflectance from Landsat, surface reflectance from MODIS, and surface reflectance from Landsat, from a 15 2 15 km region in Saskatchewan, for Landsat bands 1, 2, 3, 4, and 7. Both MODIS and Landsat images were acquired on September 17, 2001.  
Retrieved ETM+ aerosol optical thickness values from LEDAPS dataset regressed against simultaneous AERONET AOT values for the blue (0.45–0.52 m) band. (Solid line) One-to-one line. (Dashed lines) MODIS AOT uncertainties of (0:05 + 0:2 AOT).  
Article
The Landsat Ecosystem Disturbance Adaptive Processing System (LEDAPS) at the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center has processed and released 2100 Landsat Thematic Mapper and Enhanced Thematic Mapper Plus surface reflectance scenes, providing 30-m resolution wall-to-wall reflectance coverage for North America for epochs centered on 1990 and 2000. This dataset can support decadal assessments of environmental and land-cover change, production of reflectance-based biophysical products, and applications that merge reflectance data from multiple sensors [e.g., the Advanced Spaceborne Thermal Emission and Reflection Radiometer, Multiangle Imaging Spectroradiometer, Moderate Resolution Imaging Spectroradiometer (MODIS)]. The raw imagery was obtained from the orthorectified Landsat GeoCover dataset, purchased by NASA from the Earth Satellite Corporation. Through the LEDAPS project, these data were calibrated, converted to top-of-atmosphere reflectance, and then atmospherically corrected using the MODIS/6S methodology. Initial comparisons with ground-based optical thickness measurements and simultaneously acquired MODIS imagery indicate comparable uncertainty in Landsat surface reflectance compared to the standard MODIS reflectance product (the greater of 0.5% absolute reflectance or 5% of the recorded reflectance value). The rapid automated nature of the processing stream also paves the way for routine high-level products from future Landsat sensors.
 
Article
A major discovery on the coral fronts was the death of the 7000-year-old coral reefs along the Mentawai Islands located offshore of southwest Sumatra, Indonesia, in the equatorial eastern Indian Ocean due to the Indian Ocean Dipole event of 1997. Using two ocean general circulation models, the NASA Ocean Biogeochemistry Model and Estimating the Circulation and Climate of the Ocean Model, we investigate the variability in nitrate influx, mixed layer depth (MLD), and surface currents over the region 0??-8?? S; 90??-106?? E. An enhanced nitrate influx by 6.5 micromoles (3150% higher than the mean), a lower MLD by 5 m (300% lower than the mean), and a massive cyclonic eddy (400 km meridonally and 500 km zonally) are observed over the region 4??-8?? S; 94??-100?? E (along the region of coral mortality) for three months (November and December 1997 and January 1998). Cyclonic eddies enhance phytoplankton and primary productivity, but when in the proximity of a coral reef, they can destroy the coral colony through asphyxiation caused by massive phytoplankton blooms. The results bring to the fore the importance of mesoscale processes that significantly impact the health of coral reefs.
 
Article
Hard/soft classification techniques are the conventional ways of image classification on satellite data. These classifiers have a number of drawbacks. First, these approaches are inappropriate for mixed pixels. Second, these approaches do not consider spatial variability. Kriging-based soft classification (KBSC) is a nonparametric geostatistical method. It exploits the spatial variability of the classes within the image. This letter compares the performance of KBSC with other conventional hard/soft classification techniques. The satellite data used in this study is the Wide Field Sensor from the Indian Remote Sensing Satellite-1D (IRS-1D). The ground hyperspectral signatures acquired from the agricultural fields by a handheld spectroradiometer are used to detect subpixel targets from the satellite images. Two measures of closeness have been used for the accuracy assessment of the KBSC to that of the conventional classifications. The results prove that the KBSC is statistically more accurate than the other conventional techniques.
 
Entropies of the residual image É for the Cuprite scene. 
Comparison of obtained receiver operating characteristics: detection probability versus false alarm probability. 
Article
We propose a compression algorithm for hyperspectral images featuring both lossy and near-lossless compression. The algorithm is based on JPEG 2000 and provides better near-lossless compression performance than 3D-CALIC. We also show that its effect on the results of selected applications is negligible and, in some cases, better than JPEG 2000.
 
Comparison of the energy compaction of various wavelet transforms-Cuprite scene.
Rate-distortion curves for the proposed scheme and 3D-SPIHT on the Cuprite and Jasper Ridge scenes.
Performance of the proposed technique on the Cuprite scene as function of the buffer size (BIL format).
Performance of the proposed technique on the Cuprite scene as function of the buffer size (BSQ format).
Article
In this letter we propose a new technique for progressive coding of hyperspectral data. Specifically, we employ a hybrid three-dimensional wavelet transform for spectral and spatial decorrelation in the framework of Part 2 of the JPEG 2000 standard. Both onboard and on-the-ground compression are addressed. The resulting technique is compliant with the JPEG 2000 family of standards and provides competitive performance with respect to state-of-the-art techniques.
 
Article
One of the major efforts in large area land cover mapping over the last two decades was the completion of two U.S. National Land Cover Data sets (NLCD), developed with nominal 1992 and 2001 Landsat imagery under the auspices of the MultiResolution Land Characteristics (MRLC) Consortium. Following the successful generation of NLCD 1992, a second generation MRLC initiative was launched with two primary goals: (1) to develop a consistent Landsat imagery data set for the U.S. and (2) to develop a second generation National Land Cover Database (NLCD 2001). One of the key enhancements was the formulation of an image preprocessing protocol and implementation of a consistent image processing method. The core data set of the NLCD 2001 database consists of Landsat 7 Enhanced Thematic Mapper Plus (ETM+) images. This letter details the procedures for processing the original ETM+ images and more recent scenes added to the database. NLCD 2001 products include Anderson Level II land cover classes, percent tree canopy, and percent urban imperviousness at 30-m resolution derived from Landsat imagery. The products are freely available for download to the general public from the MRLC Consortium Web site at http://www.mrlc.gov.
 
Article
The biological and physical effects of hurricanes Katrina and Rita (2005) on the upper ocean are analyzed using satellite observations and model simulations of the mixed layer in the Gulf of Mexico. Along the hurricanes' passages, the Moderate Resolution Imaging Spectroradiometer and Advanced Very High Resolution Radiometer instruments detected two areas of maximum surface chlorophyll-a (chl a) concentration and sea surface cooling. These areas had peak intensities ranging from 2-3 mgmiddotm<sup>-3</sup> and 3 degC-4 degC. The depth of the mixed layer deepened by approximately 33-52 m, and the temperature of the mixed layer cooled approximately 2 degC. Hurricane wind fields intensified the oceanic cyclonic circulation, maximizing upwelling, surface cooling, and deepening the mixed layer. The forced mixed layer deepening injected nutrients into the surface layer, resulting in phytoplankton blooms three-five days later (i.e., higher chl a concentrations)
 
Article
Using aerosol optical depth (AOD at 550 nm) from the moderate-resolution imaging spectroradiometer, surface winds, outgoing long-wave radiation from National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis, and rainfall from Tropical Rainfall Measuring Mission data sets, we report a dipolelike variability in the aerosol concentration over the region (40??E-130?? E; 10?? S-10??;N) during September, October, and November 2006. Positive AOD anomalies (+ 0.4 to + 0.6) (relative to the 2000-2008 climatological average) along the equatorial East Indian Ocean and Indonesia and negative AOD anomalies (-0.2 to -0.4) over the western, northwestern, and central Indian Ocean characterize an aerosol-dipolelike variability. This east-west variability of the aerosol loading along the Indian Ocean is linked to the anomalously weak easterlies associated with the 2006 Indian Ocean Dipole event. The weaker easterlies lead to the hovering of the aerosol plume over Indonesia/Sumatra coast (98?? E), enhancing the positive anomalies of AODs, while excessive rainfall over the central Arabian Sea caused the negative AOD anomalies.
 
Classification schemes. (a) All 21 inputs feed the NN. The feature reduction is obtained by applying (b) the PCA only to the SAR imagery and considering the first component of dates (1 : 6) and (7 : 9).
Article
The 2007 data fusion contest that was organized by the IEEE Geoscience and Remote Sensing Data Fusion Technical Committee was dealing with the extraction of a land use/land cover maps in and around an urban area, exploiting multitemporal and multisource coarse-resolution data sets. In particular, synthetic aperture radar and optical data from satellite sensors were considered. Excellent indicators for mapping accuracy were obtained by the top teams. The best algorithm is based on a neural classification enhanced by preprocessing and postprocessing steps.
 
Article
A method of two-threshold expectation maximum and Markov random field is presented to automatic detection of terrain surface changes after the Wenchuan earthquake, on May 12, 2008, using multitemporal ALOS PALSAR images. As an example in the Beichuan area, three kinds of terrain surface changes, i.e., scattering enhanced, reduced, and no-changed, are automatically detected and classified. By using the tool of Google Earth, the surface change situation after the earthquake can be shown in multiazimuth views as an animated cartoon. The detection and classification are also compared with optical photographs.
 
(a) Wrapped phase map. Every cycle corresponds to half of the wavelength ( λ = 23 . 6 cm ) . (b) Mosaicking of the 25 unwrapped DInSAR maps processed to retrieve the displacement field due to the Sichuan earthquake. The area covered extends about 300 km × 250 km with six different adjacent ALOS tracks. 
Slip distribution over the (a) BQ and (b) YB faults (see Table II for details) retrieved by linear inversion of a subset of DInSAR data shown in Fig. 2(b). The black contour is the standard deviation associated to the slip distribution. The thick lines are every 2 m, while the thin lines are every 0.5 m. The red star is the hypocenter. 
Residuals between the observed and the modeled displacement for the subsampled points used for the inversion. Of the residuals, 79% are within the data error associated to each track (see Table I). 
Article
A destructive (Mw 7.9) earthquake affected the Sichuan province (China) on May 12, 2008. The seismic event ruptured approximately 270 km of the Yingxiu-Beichuan fault and about 70 km of the Guanxian-Anxian fault. Surface effects were suffered over a wide epicentral area (about 300 km E-W and 250 km N-S). We apply the differential synthetic aperture radar interferometry (DInSAR) technique to detect and measure the surface displacement field, using a set of ALOS-PALSAR L-band SAR images. We combine an unprecedented high number of data (25 frames from six adjacent tracks) to encompass the entire area which has coseismically displaced. The resulting mosaic of differential interferograms covers an overall area of about 340 km E-W and 240 km N-S. We investigate the source of the Sichuan earthquake by modeling the DInSAR data. The geometry and position of the fault parameters are inferred by a nonlinear inversion, followed by a linear inversion to retrieve the relative slip distribution. Our results show two different source mechanisms for the 145-long Yingxiu-Beichuan fault and for the 105-long Beichuan-Qingchuan fault. Both faults are characterized by slip concentrations of up to 8 m.
 
Article
This letter compares the coseismic deformation maps obtained from different synthetic aperture radar (SAR) sensors using the well-known differential SAR interferometry technique. In particular, four deformation maps have been obtained from X-, C-, and L-band SAR sensors onboard COSMO-SkyMed, Envisat, and ALOS satellite missions correspondingly. The test case is the April 6,2009, earthquake (M<sub>w</sub> = 6.3). This seismic event struck a densely populated region of the Apennines and was felt all over Central Italy. The SAR data set is rather inhomogeneous, since it includes interferograms with three different wavelengths, four acquisition geometries, different spatial resolutions, variable temporal and spatial baselines, and differently emphasized signal noise. However, we find that the detected displacements are highly comparable. The outcome of this work is that, even though such differences have an impact on the properties of the interferograms, the displacements can be measured with an overall discrepancy of about half the value of the shortest wavelength (COSMO-SkyMed) data set.
 
Article
A historic dust storm affected the eastern portions of Australia between September 22 and 24, 2009, causing significant reductions in air quality and visibility. Using multiple satellite remote sensing data sets and meteorological information, we assess the distribution of dust aerosols and their potential effects on the Earth-atmosphere system. Spaceborne active lidar data showed that dust aerosols were located up to 2 km above the surface. The thickness of the dust plume (0.55-μm aerosol optical thickness >; 1.0) reduced surface visibility to below 2 km. Dew-point depressions of 20 <;sup>;°<;/sup>;C or more occurred after passage of the dust plume, with decreases in surface temperature observed at some locations. Between the surface and 2-km level, temperature data show a cooling of ~10°C in the hours after passage of the cold front along which dust aerosols had converged. However, much of the temperature change that occurred is a result of cold air advection behind the northward traveling plume. Radiative transfer modeling suggests that only up to 1°C per day of this cooling is due to the decrease in solar radiation reaching the surface layer. Radiative transfer modeling also indicates a net warming of up to 2°C per day within and above the dust layer, possibly offsetting some cooling aloft due to the cold front passage. Modeling results indicate that expected aerosol radiative effects to temperature are small compared to synoptic influences and are unlikely to be sampled in observations under this scenario since the magnitudes of these effects are quite small.
 
Article
The Stratospheric WAter vapor RAdiometer (SWARA) is a microwave radiometer designed for ground-based measurements of water vapor (H<sub>2</sub>O) in the middle atmosphere (20 to 80 km), including the stratosphere and mesosphere. The instrument is operating in a noncryogenic balancing calibration mode. Since its deployment, features have been observed in the spectrum which can be attributed to resonant variations of the antenna pattern of the corrugated horn. This paper presents copolar and crosspolar antenna pattern measurements of two sister antennas of the SWARA horn, as well as water vapor measurements from both antennas on the ground-based microwave radiometer MI ddle Atmospheric W Ater vapor RA diometer. We show that small irregularities in the frequency spectrum at the -20-dB level are visible in the copolar pattern, which, due to the balancing operation scheme used for the radiometer, lead to features in the spectrum that have the same or even higher brightness temperature as the line of interest.
 
Quality of water in the Lake Päijänne region (based on ground truth data from 1994 to 1997). White areas are lakes that are not classified. The width of the area is 100 km.
Modis channel 1 radiance (watts per square meter per micrometer per steradian) on August 27, 2000.
Normalized histograms of MODIS radiances (August 27, 2000) found within each ground truth water quality class (data from 1994 to 1997).
Article
The traditional method used in the water quality classification of Finnish lakes includes the collection of water samples from lakes and their analysis in laboratory conditions. The classification is based on statistical analysis of water quality parameter values and on expert opinion. It is possible to acquire similar information by using radiance values measured with the Earth Observing System Terra/Aqua Moderate Resolution Imaging Spectroradiometer (MODIS). In this letter, the classification accuracy with MODIS data is about 80%. Only about 0.2% of the 20 391 pixels were misclassified by two or more classes, as a four-class classification system is used.
 
Article
China's Feng Yun-3A (FY-3A) meteorological satellite is a second-generation polar-orbiting meteorological satellite launched in May 2008. The Microwave Humidity Sounder (MWHS) is the main payload, designed for atmospheric humidity sounding. Before the launch of MWHS, a series of experiments was conducted in a thermal/vacuum (T/V) chamber. This letter describes the MWHS T/V calibration, in which the flight model currently operating on FY-3A was tested. The calibration procedure and data-processing methods are presented. Calibration results, such as radiometric resolution, receiver nonlinearity, and calibration bias, were obtained. The results meet the specifications on bias and sensitivity of MWHS. Since the instrument temperatures will be approximately 10°C-20°C on orbit, the calibration errors of MWHS over the range of 100-300 K would be less than 0.3 K using the nonlinearity coefficients derived in the T/V test.
 
Part of the MERIS browse image of orbit 11528 (May 14, 2004). The approximate location of the satellite measurements is shown by a box. 
Relative difference between SCIAMACHY and MERIS top-of- atmosphere reflectances as the function of the longitude for selected MERIS channels. 
Article
This letter is aimed at better understanding of Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) reflectance radiometric calibration errors using the Medium Resolution Imaging Spectrometer (MERIS) onboard ENVISAT. Earlier investigations showed that the SCIAMACHY calibration error can reach 20% in the visible bands, which prevents aerosol retrievals using the SCIAMACHY data. Recent improvements of the SCIAMACHY calibration are discussed. It is found that the differences in reflectances for the wavelengths 443, 560, 665, 754, and 865 nm between MERIS and improved Processor 6 SCIAMACHY data are close to the MERIS radiometric calibration error, which is below 4%
 
Article
High-resolution and dual polarized Spotlight TerraSAR-X images are assessed for soil moisture parameter retrieval. This letter presents bare soil moisture estimation and estimation of moisture of vegetated areas. The bare soil moisture estimation is based on the Shi model. The Minimum Mean Square Error approach is used to determine the unknown parameters of the Shi model using ground measurements of volumetric moisture and SAR data. The soil moisture of vegetated areas is estimated using the vegetation and soil backscattering coefficients. The unknown parameters of vegetation and soil backscattering models were estimated using Tikhonov optimization. The experimental results showed that the used models provide good results for estimating bare soil moisture and moisture of vegetated areas.
 
Zero statistics for an example elevation cut.
Histogram of difference values for radial 185. Fig 2. Histogram of range bin values for KBIS radial 185.
Article
Weather radar products from the U.S. National Weather Service (NWS) are used by the government and private sectors. Very high resolution radar data are increasingly being utilized in real time. However, the bandwidth needed to transmit these data (termed level-II super-resolution data) from the radar to the destination site is a limiting issue. General-purpose compression programs are not tuned to the properties of weather radar data. As the NWS continues to upgrade the capabilities of radar network, the amount of data will continue to increase. As a result, compression is of vital interest to keep down maintenance, storage, and transmission costs. A method for lossless compression of these data on a radial-by-radial basis focusing on the delta (difference) between range bins of super-resolution radar data is presented and is called super-resolution delta compression (SRDC). There are several specialized aspects of SRDC that are based on the properties of weather radar data. SRDC was tested on level-II reflectivity product data from several S-band Doppler weather radars in the NWS network and was compared with two general-purpose compression programs and a different weather-radar-specific compression approach. The results show that the newly developed SRDC yield is approximately 17% better than the next best approach and approximately 47% better than only preprocessed radials.
 
(a) Δ SST current given in the AATSR L2 files in a part of North Atlantic for nighttime measurements and best quality pixels (May 26, 2008; contour plot identifies the two values, namely, − 0.13 K and − 0.07 K). (b) Δ SST model computed by model (3) on the same data. 
Article
The Advanced Along-Track Scanning Radiometer (AATSR) onboard Envisat is designed to provide very accurate measurements of sea surface temperature (SST). Using colocated in situ drifting buoys, a dynamical matchup database (MDB) is used to assess the AATSR-derived SST products more precisely. SST biases are then computed. Currently, Medspiration AATSR SST biases are discrete values and can introduce artificial discontinuities in AATSR level-2 SST fields. The new AATSR SST biases presented in this letter are continuous. They are computed, for nighttime and best proximity confidence data, by linear regression with different MDB covariables (wind speed, latitude, aerosol optical depth, etc.). As found, the difference between dual-view and nadir-only SST products explains most of the variability (26%).
 
Article
The top-of-atmosphere reflectance measurements by advanced along-track scanning radiometer (AATSR), medium-resolution imaging spectrometer (MERIS), and scanning imaging absorption spectrometer for atmospheric chartography (SCIAMACHY) onboard ENVISAT have been compared for collocated scenes. The AATSR and MERIS observations were averaged to the scale of a SCIAMACHY ground scene (30 km times 60 km). The SCIAMACHY reflectances were averaged to account for much coarser spectral resolution of AATSR and MERIS observations. It was found that SCIAMACHY reflectances coincide with those of MERIS within 4% MERIS calibration error. This is also the case for AATSR reflectances, except at the wavelength of 0.865 mum, where SCIAMACHY gives, on average, 6% lower reflectances as compared to those of AATSR. They are 3% too low as compared to MERIS observations at this wavelength.
 
Correlation between AATSR and SCIAMACHY reflectances at 550 nm. 
Correlation between AATSR and SCIAMACHY reflectances at 870 nm. 
Article
This letter investigates the synergy between the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) and the Advanced Along Track Scanning Radiometer (AATSR) onboard the ENVISAT platform for reflectance calibration purposes. This calibration study was mainly performed over a portion of a hurricane corresponding to fully cloudy SCIAMACHY and AATSR pixels. Results show that SCIAMACHY underestimates the top-of-atmosphere (TOA) reflectance by up to 23% (at 870 nm) as compared to AATSR for a nadir viewing geometry. Specifically, considering AATSR calibration as accurate, which is confirmed by comparison with the Medium Resolution Imaging Spectrometer, the SCIAMACHY TOA reflectances should be multiplied by 1.21, 1.19, 1.23, and 1.10 for wavelengths at 550, 670, 870, and 1600 nm, respectively, ahead of satellite retrieval schemes based on the measurements of TOA reflectance
 
Article
This letter presents new models for estimating clear-sky instantaneous longwave radiation over land surfaces using the Geostationary Operational Environmental Satellites (GOES) Sounders and GOES-R Advanced Baseline Imager (ABI) thermal infrared top-of-atmosphere (TOA) radiances. The method used in this study shares the same hybrid method framework designed for Moderate Resolution Imaging Spectroradiometer. We propose separate surface downward longwave radiation (LWDN) and upwelling longwave radiation (LWUP) models because the two components are dominated by different surface/atmospheric properties. A nonlinear model was developed to estimate LWDN, and a linear model was developed to estimate LWUP. The GOES-12 Sounder-derived LWDN, LWUP, and surface net longwave radiation (LWNT = LWUP-LWDN) were evaluated using one full-year of ground data from the Surface Radiation Budget Network. The root-mean-squared errors (rmses) are less than 22.03 W/m<sup>2</sup> at all four sites. Our study indicates that the hybrid method can also be applied to estimate LWUP using the future GOES-R ABI TOA radiances. The lack of a channel beyond 13.3 m in the proposed ABI design may cause larger rmses when estimating LWDN.
 
Article
This letter presents a novel approach for on-orbit characterization of MODerate resolution Imaging Spectroradiometer (MODIS) band-to-band registration (BBR) using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) aboard the Terra spacecraft. The spatial resolution of ASTER spectral bands is much higher than that of MODIS, making it feasible to characterize MODIS on-orbit BBR using their simultaneous observations. The ground target selected for on-orbit MODIS BBR characterization in this letter is a water body, which is a uniform scene with high signal contrast relative to its neighbor areas. A key step of this approach is to accurately localize the measurements of each MODIS band in an ASTER measurement plane coordinate (AMPC). The ASTER measurements are first interpolated and aggregated to simulate the measurements of each MODIS band. The best measurement match between ASTER and each MODIS band is obtained when the measurement difference reaches its weighted minimum. The position of each MODIS band in the AMPC is then used to calculate the BBR. The results are compared with those derived from MODIS onboard Spectro-Radiometric Calibration Assembly. They are in good agreement, generally less than 0.1 MODIS pixel. This approach is useful for other sensors without onboard spatial characterization capability.
 
Article
A three-year time-series of radiometric data collected with an autonomous above-water system at the Acqua Alta Oceanographic Tower in the northern Adriatic Sea has shown its applicability for monitoring the trophic state of marine waters and its suitability for the validation of remote sensing products in coastal areas. Specifically, the radiometric data have been used to produce surface chlorophyll a concentration (Chla) by applying a regional algorithm proposed for the northern Adriatic Sea coastal waters. A comparison based on 41 match-ups between these Chla and reference values from high-performance liquid chromatography, has shown an average absolute difference of 32%. The comparison of Chla derived from remote sensing SeaWiFS and in situ above-water radiances has shown an average absolute difference of 21% for 183 match-ups, when the same regional algorithm is applied to both types of radiometric data.
 
Article
For measurements that are made by the CALIPSO lidar, the layer-integrated attenuated backscatter of opaque water clouds gamma'<sub>water,O</sub> can be accurately estimated for those cases for which there is no overlying aerosol or cloud layer. When transparent overlying layers of clouds or aerosols are present, the layer-integrated attenuated backscatter that is measured for the water cloud is reduced by a factor that is equal to the two-way transmittance of the upper layer. Because the layer-integrated depolarization ratio can be used to obtain an independent estimate of gamma'<sub>water,O</sub>, we can subsequently derive both the optical depth and an estimate of the layer-averaged lidar ratio of the overlying layer.
 
Article
We investigated the influence of a wire grid above a paved ground on thermal brightness at 1.4 GHz. Reflectivities were derived from dual-polarized brightness temperature measurements for different grid orientations and wire spacings between 2.5 and 20 cm. For spacings larger than a quarter of a wavelength (≈5 cm), the grid had no impact on the observed reflectivities. A physical model was used to analyze the experimental results.
 
Article
Satellite imagery classification using the support vector machine (SVM) algorithm may be a time-consuming task. This may lead to unacceptable performances for risk management applications that are very time constrained. Hence, methods for accelerating the SVM classification are mandatory. From the SVM decision function, it can be noted that the classification time is proportional to the number of support vectors (SVs) in the nonlinear case. In this letter, four different algorithms for reducing the number of SVs are proposed. The algorithms have been tested in the frame of a change detection application, which corresponds to a change-versus-no-change classification problem, based on a set of generic change criteria extracted from different combinations of remote sensing imagery.
 
Article
There is a large uncertainty in the estimation of dust radiative forcing due to the lack of adequate data about complex spatial and temporal pattern of the radiative properties of dust. Here, we examine the temporal and spatial variability of dust absorption in the thermal infrared over the Afro-Asian regions using satellite data. Large dust absorption (nearly double compared to that of pure dust) was observed in regions with large anthropogenic influence, possibly due to deposition of black carbon on dust particles. While most of the recent estimates of global mean dust radiative forcing predicted net cooling, our studies indicate that there could be large heating due to dust over vast Afro-Asian regions. It appears that large dust heating is due to its interaction with anthropogenic black carbon
 
Article
The importance of aerosol absorption in satellite sensor vicarious calibration and/or satellite measurement of physical parameters is reiterated in a sensitivity study performed using a radiative transfer model, with field-measured data as input. Broadband shortwave surface fluxes need to be measured according to new protocols, described herein, to infer atmospheric absorption to improve calibration accuracy to within the plusmn2% stated goal of next-generation sensors such as Visible/Infrared Imager/Radiometer Suite.
 
Article
A method previously developed by the authors is employed to determine the cloud geometrical thickness from combined measurements of the cloud brightness temperature and the backscattered solar light intensity in the O<sub>2</sub> A-band. The technique is applied to the analysis of four selected orbits of the European Remote Sensing 2 satellite using measurements performed by the Global Ozone Measurement Experiment spectrometer and the Along Track Scanning Radiometer. Cloud geometrical thicknesses were found to be in the range 0.5-7.5 km with most frequent values of 3 km for the cases studied.
 
Article
We propose a low false alarm methodology to determine anomalies in hyperspectral data. The method is based on the assumptions that the linear mixing model is valid and that, due to the resolution of the image, most pixels are mixtures of common substances, of which pure pixels (not mixtures) are rare. In the first stage of the algorithm, the classes associated with the background, which are the dominant classes in the image, are found by clustering the image pixels. The resulting clusters may be considered as representatives of the background classes in the image. In order to determine the anomalous pixels, a threshold may be applied to the distance between the pixel spectrum and the cluster centers. However, pixels corresponding to anomalies and pure substances will both show high distances. If we consider that the background classes are themselves most likely mixtures of other materials, the pixels within the convex hull formed by the background classes will have positive fractions that are smaller than one. The pure substances, however, will be outside such a convex hull and will show negative or superunity fractions. Pixels with such mixing proportions are explained as linear combinations of the background classes and, therefore, as not true anomalies. Pixels corresponding to anomalies, however, when expressed as linear combinations of the background classes, show high residual error even with negative and superunity mixing proportions. We use the unmixing spectral linear model without the nonnegativity constraint to distinguish between false anomalies corresponding to pure substances and real man-made anomalies.
 
Article
The Altimetric Bathymetry from Surface Slopes (ABYSS), which is the proposed science payload on the International Space Station (ISS), is a Johns Hopkins University Applied Physics Laboratory-developed flight-proved delay-Doppler phase-monopulse radar altimeter capable of measuring ocean surface slope in the 6-200-km half-wavelength frequency band range with an accuracy of 0.5 mu rad , with autonomous gimbal control to compensate for the ISS structural motions. This measurement allows an improved mapping of the global bathymetry, enabling a wide range of scientific research works and applications. The nonrepeat ISS orbital ground track is ideal for ABYSS. This letter describes a simulation study on the effects of the Earth's gravity field and other errors, including thermal bending of the ISS, on the orbit determination of the altimeter instrument antenna phase center location, fulfilling the science objectives of ABYSS. Our study concluded that the error due to mean gravity field is no longer limiting due primarily to the recent Gravity Recovery and Climate Experiment gravity modeling and that the ABYSS/ISS radial orbit slope error budget in the presence of various force and measurement model errors is estimated at the 0.2-mu rad root-sum-squared (RSS) level, which satisfies the ABYSS orbit accuracy science requirement to provide an improved mapping of global bathymetry.
 
Article
In this letter, a simulation procedure for airborne stripmap synthetic aperture radar with zero squint angle is proposed. The procedure is based on the idea of inverse processing and 1-D summation. It utilizes narrow bandwidth approximation and is more efficient compared to a time-domain simulator. Moreover, it allows for the simulation of raw data for higher aperture angle configurations compared to existing approaches. The effectiveness of the approach is demonstrated by means of examples for point scatterers.
 
Article
We study the retrieval of surface and deep moisture of bare soil from noisy radar observations using simulated annealing. Due to moisture variations with depth, we model bare soil with a stratified dielectric profile with a rough surface on top. Small perturbation method (SPM) is used as the forward model. We use the full moisture profile for radar data synthesis and study the retrieval accuracy by varying the number of layers that represent the soil profile during inversion. The effect of measurement frequency on the accuracy of deep moisture retrieval is investigated. This work is intended for assessing the effect of subsurface profile on soil moisture retrieval from radar observations of NASA's Soil Moisture Active and Passive (SMAP) mission and future lower frequency airborne or spaceborne systems that may follow SMAP.
 
Impact of radiometric bias on the two-class problem. (Black line) Original distribution of the training classes. (Gray line) Radiometric bias of 1 dB. Due to the shift in pdfs, the decision threshold derived during the training phase no longer represents the optimal threshold in the maximum-likelihood sense. 
Article
The choice of synthetic aperture radar (SAR) system design parameters such as radiometric calibration uncertainty and noise-equivalent sigma zero has a significant impact on applications exploiting SAR image data. However, methods for quantitatively translating the impact of system and mission parameter choices into the application context are lacking. This letter addresses this subject and derives a closed-form algebraic expression for translating radiometric biases due to calibration uncertainties-an important SAR engineering specification-into estimates of classification uncertainties for the restricted case of two homogeneous classes characterized by different backscatter intensity levels. The expression is exploited within this letter to estimate the potential impact of radiometric uncertainty on SAR-derived thematic maps. The results indicate that classification results based on the joint use of data from future SAR constellations in particular may be significantly degraded due to calibration uncertainties.
 
(a) Location of the Mae Sa watershed. (b) Distribution of the micrometeorological and rain gauge stations in Mae Sa. 
Flowchart of the TSEBM module. micrometeorological stations and are used as references in comparing with the estimations derived from satellite images. The following types of satellite images are used: Landsat-5 Thematic Mapper (TM) (acquired on February 07, 2005 Landsat-7 Enhanced TM Plus (ETM+) (April 07, 2006, January 04, 2007, January 20, 2007, April 10, 2007, and February 24, 2008), and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) (February 02, 2006, and February 08, 2008) images from the Land Processes Distributed Active Archive Center, U.S. Geological Survey. Two DEMs are utilized for terrain correction. DEM_map is generated from digitizing contours of a 1 : 50 000 topographical map prepared by the Royal Thai Survey Department in 1994. DEM_ASTER is the ASTER DEM product, which is the 20080208 AST14DMO (Digital Elevation Model & Registered Radiance at the Sensor-Orthorectified) imagery. The resolutions of DEM_map and DEM_ASTER are, respectively, 20 and 30 m.
Comparison between annual average net radiation and soil heat flux measured at the meteorological station (site #429) in 2008. 
Article
Evapotranspiration (ET) plays a major role in the energy and water balances of the hydrological cycle. Monitoring ET at a regional level has become feasible with the advance of remote-sensing technology. This letter presents a module that incorporates satellite images, surface meteorological data, and topographic information in estimating ET over a tropical montane watershed. The satellite images used include Thematic Mapper (TM), Landsat-7 Enhanced Thematic Mapper Plus, and Advanced Spaceborne Thermal Emission and Reflection Radiometer with visible, near infrared, shortwave infrared, and thermal infrared bands. The estimated surface energy fluxes are compared with the in situ measurements. The results demonstrate that, compared to other model estimations, the proposed module with terrain correction provides the highest correlation ( r = 0.75) between the estimated latent heat flux associated with ET and its corresponding in situ measurement. The proposed module will be further refined and applied to monitor long-term ET over mountainous watersheds.
 
Shift estimation error (standard deviation) in units of resolution elements as a function of coherence . The error is normalized to N = 1. (Bold line) Coherent cross correlation and CRB theory according to (1) and simulation results (dots). (Dashed line) Incoherent cross correlation, simulation results (dots connected by dashed line). (Thin line) Split-bandwidth estimator for b = 0:5 B; theory according to (5) and simulation results (circles). Note:  
Split-bandwidth interferometry is an approach to estimate the phase slope between a lower and an upper subband.  
Range estimation error ratio from (6) of the split-bandwidth method or a Delta-k system as a function of subband-to-bandwidth ratio b=B.  
(a) Improved Delta-k system. The transmit pulse contains two sequences with their spectral energy placed close to the limits of the system bandwidth. (b) The received signal may be sampled and stored with one-third of the full sampling frequency f without aliasing.  
Shift estimation error in units of resolution elements for a single point scatterer in incoherent clutter as a function of the SCR (in decibels).  
Article
Estimation of differential shift of image elements between two synthetic aperture radar (SAR) images is the basis for many applications, like digital elevation model generation or ground motion mapping. The shift measurement can be done nonambiguously on the macro scale at an accuracy depending on the range resolution of the system or on the micro scale by employing interferometric methods. The latter suffers from phase cycle ambiguities and requires phase unwrapping. Modern wideband high-resolution SAR systems boast resolutions as small as a few tens of a wavelength. If sufficiently many samples are used for macro-scale shift estimation, the accuracy can be increased to a small fraction of a resolution cell and even in the order of a wavelength. Then, accurate absolute ranging becomes precise enough to support phase unwrapping or even make it obsolete. This letter establishes a few fundamental equations on the accuracy bounds of shift estimation accuracy for several algorithms: coherent speckle correlation, incoherent speckle correlation, split-band interferometry, a multifrequency approach, and correlation of point scatterers in clutter. It is shown that the performance of split-band interferometry is close to the Crame´r-Rao bound for a broad variety of bandwidth ratios. Based on these findings, Delta-k systems are proposed to best take advantage of the available radar bandwidth.
 
Top-cited authors
Gustau Camps-Valls
  • University of Valencia
Jocelyn Chanussot
  • Grenoble Institute of Technology
Jon Atli Benediktsson
  • University of Iceland
Qian Du
  • Mississippi State University
Liangpei Zhang
  • Wuhan University