Paco Lopez-Dekker

Tandem-L: A Highly Innovative Bistatic SAR Mission for Global Observation of Dynamic Processes on the Earth's Surface

Tandem-L is a proposal for a highly innovative L-band SAR satellite mission for the global observation of dynamic processes on the Earths surface with hitherto unparalleled quality and resolution. It is based on the results of a pre-phase A study which started in 2013 and is currently undergoing a phase-A study. Thanks to the novel imaging techniques and the vast recording capacity with up to 8 terabytes/day, it will provide vital information for solving pressing scientific questions in the biosphere, geosphere, cryosphere, and hydrosphere. By this, the new L-band SAR mission will make an essential contribution for a better understanding of the Earth system and its dynamics. Tandem-L will, moreover, open new opportunities for risk analysis, disaster management and environmental monitoring by employing especially designed acquisition modes and techniques in combination with a reconfigurable tandem satellite configuration and an L-band SAR instrument with advanced digital beamforming techniques.

On Some Spectral Properties of TanDEM-X Interferograms Over Forested Areas

This letter reports about some observations over rainforests (in Brazil and Indonesia), where the spectra of TanDEM-X interferograms show distinct features, almost a signature, which is explained and modeled in terms of the scattering properties. Supported by comparisons with simulations, the observations exclude any homogeneous horizontally layered forest; instead, they are compatible with a model with point scatterers clustered in clouds. Such a model, with high extinction and large gaps that allow significant penetration, is able to explain to a good degree the observations.

TanDEM-X First DEM Acquisition: A Crossing Orbit Experiment

This letter describes the first interferometric acquisitions and results obtained by the TerraSAR-X add-on for Digital Elevation Measurements mission. Due to the large along-track separation between the two satellites during the approaching maneuver and the Earths rotation, useful interferometric acquisitions were only possible at high latitudes. This resulted in a crossing angle between the ground tracks whose impact was corrected by acquiring the two synthetic-aperture radar images with an opposite squint. The still very large 2-km cross-track baseline resulted in a 3.8-m interferometric height of ambiguity, producing extremely detailed images of the topography of the target area. Results acquired over the October Revolution Island, Russia, are shown and discussed.

MIMO-SAR and the orthogonality confusion

This paper reviews radar architectures that employ multiple transmit and multiple receive channels to improve the performance of synthetic aperture radar (SAR) systems. These advanced architectures have been dubbed multiple-input multiple-output SAR (MIMO-SAR) in analogy to MIMO communication systems. Considerable confusion arose, however, with regard to the selection of suitable waveforms for the simultaneous transmission via multiple antennas. In this paper, it is shown that the mere use of orthogonal waveforms is insufficient for the desired performance improvement in view of most SAR applications. As a solution to this fundamental MIMO-SAR problem we had previously suggested to exploit the special data acquisition geometry of a side-looking imaging radar equipped with multiple receiver channels in addition to appropriately designed waveforms transmitted by multiple antennas. Here, we extend this approach to a more general set of radar waveforms with special correlation properties that satisfy a short-term shift-orthogonality condition. We show that the echoes from simultaneously transmitted pulses can be separated if the short-term shift orthogonality is combined with digital beamforming on receive in elevation. This enables the implementation of a fully functional MIMO-SAR without correlation noise leakage for extended scattering scenarios.

Contrast-Based Phase Calibration for Remote Sensing Systems With Digital Beamforming Antennas

A contrast-based phase calibration algorithm for digital beamforming remote sensing radars using three contrast metrics is presented. The algorithm corrects time-varying antenna array phase errors that defocus digital beamforming remote sensing radar imagery. Amplitude errors are treated by equalizing the received powers in all elements. As such, the algorithm does not produce an absolute (or radiometric) calibration vector for the array. The performance of the algorithm is studied using a combination of simulated and real radar data under various conditions and is compared with a clutter-based calibration algorithm. An analytical proof showing that maximizing the expected value of the 4-norm metric is equivalent to phase-calibrating the image, except for a linear phase offset, is provided. We find that the clutter calibration algorithm performs best for statistically homogeneous scenes but that the contrast-calibration algorithms perform better with scenes with larger contrast ratios.

Tandem-L: And innovative interferometric and polarimetric SAR mission to monitor earth system dynamics with high resolution

Tandem-L is a proposal for an innovative interferometric and polarimetric radar mission that enables the systematic monitoring of dynamic processes on the Earth surface. Important mission objectives are global forest height and biomass inventories, large scale measurements of millimetric displacements due to tectonic shifts, and systematic observations of glacier movements. The innovative mission concept and the high data acquisition capacity of Tandem-L provide a unique data source to observe, analyze and quantify the dynamics of a wide range of mutually interacting processes in the bio-, litho-, hydro- and cryosphere. By this, Tandem-L will be an essential step to advance our understanding of the Earth system and its intricate dynamics.

Signal: SAR for ice, glacier and global dynamics

SIGNAL is an innovative earth exploration mission proposal with the main objective to estimate accurately and repeatedly topography and topographic changes associated with mass change or other dynamic effects on glaciers, ice caps and polar ice sheets. Elevation measurements are complemented with glacier velocity measurements, providing valuable additional information for a better understanding of the hydrology of glacierized basins and of the Arctic and Antarctic water cycle. SIGNAL is capable of monitoring all critical regions with a high spatial resolution and an adequate revisit time. This paper gives an overview about the actual mission design status and provides a brief description of the topography (DEM - digital elevation map) self-calibration strategy and the estimated global interferometric performance.

BIOMASS end-to-end mission performance simulator

This paper discusses the implementation of an end-to-end simulator for the BIOMASS mission. An overview of the system architecture is provided along with a functional description of the modules that comprise the simulator.

Approach to velocity and acceleration measurement in the Bi-Directional SAR imaging mode

This paper presents an initial analysis of the possibilities for velocity and acceleration measurement with the Bi-Directional SAR imaging mode (BiDi). It comprises single satellite single path acquisitions as well as a constellation of two satellites. The translational velocity components into azimuth and range directions are simulated. A BiDi approach for measuring the azimuth velocity from one satellite with one receiving channel is proposed. Image examples acquired with the TerraSAR-X (TSX) and TanDEM-X (TDX) satellites show velocity and acceleration effects on ships and the proposed BiDi velocity approach is verified. Interferometric fringes were observed on anchoring ships. A first approach into the understanding of rotational effects was achieved by simulation of rotational fringes.

Biomass End-to-End mission performance assessment

This paper provides an overview of the BIOMASS Mission End-to-End simulator (BEES) and of the mission performance analysis performed with it. The end-to-end performance, in terms of biomass estimates error, is close to the 20% error goal set for the mission. The main sources of errors are temporal decorrelation and the limited available bandwidth, while system induced errors have a negligible impact on the final performance.