Statistics for Spatial Data.

[1] The Shuttle Radar Topography Mission produced the most complete, highest-resolution digital elevation model of the Earth. The project was a joint endeavor of NASA, the National Geospatial-Intelligence Agency, and the German and Italian Space Agencies and flew in February 2000. It used dual radar antennas to acquire interferometric radar data, processed to digital topographic data at 1 arc sec resolution. Details of the development, flight operations, data processing, and products are provided for users of this revolutionary data set.

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The Shuttle Radar Topography Mission

Temporal and geometrical decorrelation often prevents SAR interferometry from being an operational tool for surface deformation monitoring and topographic profile reconstruction. Moreover, atmospheric disturbances can strongly compromise the accuracy of the results. The authors present a complete procedure for the identification and exploitation of stable natural reflectors or permanent scatterers (PSs) starting from long temporal series of interferometric SAR images. When, as it often happens, the dimension of the PS is smaller than the resolution cell, the coherence is good even for interferograms with baselines larger than the decorrelation one, and all the available images of the ESA ERS data set can be successfully exploited. On these pixels, submeter DEM accuracy and millimetric terrain motion detection can be achieved, since atmospheric phase screen (APS) contributions can be estimated and removed. Examples are then shown of small motion measurements, DEM refinement, and APS estimation and removal in the case of a sliding area in Ancona, Italy. ERS data have been used.

Permanent scatterers in SAR interferometry

We present a new differential synthetic aperture radar (SAR) interferometry algorithm for monitoring the temporal evolution of surface deformations. The presented technique is based on an appropriate combination of differential interferograms produced by data pairs characterized by a small orbital separation (baseline) in order to limit the spatial decorrelation phenomena. The application of the singular value decomposition method allows us to easily "link" independent SAR acquisition datasets, separated by large baselines, thus increasing the observation temporal sampling rate. The availability of both spatial and temporal information in the processed data is used to identify and filter out atmospheric phase artifacts. We present results obtained on the data acquired from 1992 to 2000 by the European Remote Sensing satellites and relative to the Campi Flegrei caldera and to the city of Naples, Italy, that demonstrate the capability of the proposed approach to follow the dynamics of the detected deformations.

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A new algorithm for surface deformation monitoring based on small baseline differential SAR interferograms

On February 22, 2000 Space Shuttle Endeavour landed at Kennedy Space Center, completing the highly successful 11-day flight of the Shuttle Radar Topography Mission (SRTM). Onboard were over 300 high-density tapes containing data for the highest resolution, most complete digital topographic map of Earth ever made. SRTM is a cooperative project between NASA and the National Imagery and Mapping Agency (NIMA) of the U.S. Department of Defense. The mission was designed to use a single-pass radar interferometer to produce a digital elevation model (DEM) of the Earth's land surface between about 60 deg north and 56 deg south latitude. When completed, the DEM will have 30 m pixel spacing and about 15 m vertical accuracy. Two orthorectified image mosaics (one from the ascending passes with illumination from the southeast and one from descending passes with illumination from the southwest) will also be produced.

Introduction: The Cassini Titan Radar Mapper [1] acquired microwave reflectivity and emissivity measurements of Titan’s surface using scatterometer and radiometer modes on five recent flybys. The scatterometer uses a 0.38° antenna beam at 13.78 GHz (2.17 cm) in an active, real-aperture mode to produce regional-scale backscatter images across large areas of the surface. Radiation at this wavelength penetrates the thick atmosphere and permits surface measurements at resolutions from 10 to 200 km. Raster scanning achieves large angular coverage of the surface to properly sample the average backscatter function. A backscatter function over a wide range of angles reveals much about the dielectric composition, surface and subsurface scattering properties. The radiometer mode operates in tandem with the active mode, passively receiving and measuring the brightness of Titan's emission in between the pulsed echoes of the scatterometer data. Thus, it measures emission from the same area of the surface, at the same linear polarization, as the active mode data. The radar’s active and passive modes individually contribute essential information about an area of coverage. Yet, when taken together, the different radar data types reveal a more complete story, providing complementary information on the physical and electrical properties of the surface. Here we present overlapping data collected by the RADAR’s scatterometer and radiometer over the Titan observations to-date (denoted Ta-Inbound and Ta-Outbound, October 2004; T3, February 2005; T4, March 2005; T7, September 2005; T8-Inbound and T8-Outbound, October 2005). We present here separate model solutions obtained from the active and passive data in terms of electrical and physical properties. We are now beginning to reconcile the implications of the two using a unified surface model, and include preliminary results of this modeling approach. Active Model: We use angle diversity to separate a quasispecular surface scattering term from a diffuse volume scattering term in the radar echo. We model the observed backscatter using traditional scattering models: a Hagfors’ [2] or Gaussian [3] specular term plus a cosine^n diffuse component (Figure 1). The parameters of the best fit specular component suggest values for the dielectric constant and rms surface slope of the observed area. For much of the surface, we retrieve dielectric constants ranging from 1.5 to greater than 3. Surface slope distributions range from a few degrees rms up to 15 degrees in different regions. We note that these values represent average measurements over a variety of terrains and it is possible none of the surfaces scatters in this average way. Nonetheless, these results begin to constrain the range of materials and surface conditions that are found on Titan.

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MODELING TITAN'S SURFACE FROM CASSINI RADAR'S SCATTEROMETER AND RADIOMETER MEASUREMENTS. L. C. Wye

Edgelist phase unwrapping algorithm for time series

In InSAR time series analysis, persistent scatterers (PS) are pixels that remain temporally correlated even in areas of otherwise high decorrelation. Using these stable pixels as reference points, we can analyze deformation signals on the Earth’s surface down to the millimeter scale. PS possess different physical and statistical properties compared to the background, and analyzing the statistical behavior of PS can help to elucidate radar backscattering behavior from different terrain. Here, we propose a new statistical characterization of SAR image power using a mixture distribution of PS and non-PS points, i.e. clutter. We find that a lognormal distribution fits both pixel types, validated by a scattering model that is a function of bandwidth. We present here from C-band RADARSAT-2 data, and will compare these with additional C-band Sentinel data and L-band data from ALOS-2.

SAR Image Statistics by Bandwidth Using a Mixture Distribution of Persistent Scatterer and Clutter Distributions

In order to understand L-band multipolarization radar measurements of forested areas, a model for the forest polarization signature was developed. The model is based on backscatter from dielectric cylinders which represent branches and trunks. In the model the Stokes matrices corresponding to several different scattering mechanisms is calculated, combining the results to get the total Stokes matrix. Comparison of model predictions with radar measurements shows that the model can accurately predict the forest polarization signature.

Application Of Radar Polarimetry To Forestry

During multisensor experiments in the Oregon Transect Ecosystem Research (OTTER) project, the JPL AIR-SAR collected data over six study sites in western Oregon. The SAR flights took place in June and August 1990 and March 1991. The sites ranged from the dense forests of the coastal region to the sparse inland Juniper forests, thus providing a wide range of above-ground biomass values (8 Tons/HA to 960 Tons/HA). The authors have previously reported the results of studying the polarimetric SAR data from June 1990. They concentrate on March 1991 data. These data were obtained under flooded conditions and colder temperatures. The variations of radar backscatter with biomass and other forest parameters are studied and compared to those from June 1990. Differences between radar backscatters of several dB have been observed. The authors' observations substantiate their earlier findings that the radar measurements cannot be used to uniquely obtain the biomass, and that instead, inversion algorithms to find the fundamental scattering properties of forest components need to be used. >

Howard A. Zebker

Papers

MODELING TITAN'S SURFACE FROM CASSINI RADAR'S SCATTEROMETER AND RADIOMETER MEASUREMENTS. L. C. Wye

Edgelist phase unwrapping algorithm for time series

SAR Image Statistics by Bandwidth Using a Mixture Distribution of Persistent Scatterer and Clutter Distributions

Application Of Radar Polarimetry To Forestry

Effects of environmental change on radar backscatter in the Oregon Transect