Development of the TanDEM-X Calibration Concept: Analysis of Systematic Errors

The TanDEM-X mission, result of the partnership between the German Aerospace Center (DLR) and Astrium GmbH, opens a new era in spaceborne radar remote sensing. The first bistatic satellite synthetic aperture radar mission is formed by flying the TanDEM-X and TerraSAR-X in a closely controlled helix formation. The primary mission goal is the derivation of a high-precision global digital elevation model (DEM) according to High-Resolution Terrain Information (HRTI) level 3 accuracy. The finite precision of the baseline knowledge and uncompensated radar instrument drifts introduce errors that may compromise the height accuracy requirements. By means of a DEM calibration, which uses absolute height references, and the information provided by adjacent interferogram overlaps, these height errors can be minimized. This paper summarizes the exhaustive studies of the nature of the residual-error sources that have been carried out during the development of the DEM calibration concept. Models for these errors are set up and simulations of the resulting DEM height error for different scenarios provide the basis for the development of a successful DEM calibration strategy for the TanDEM-X mission

Antenna Modeller for Synthetic Aperture Radar Applications. Electromagnetic and Radiometric Considerations

The objective of the present Master Thesis is designing an optimizer of the excitation coefficients of a phased array antenna

Offshore oil spill detection using synthetic aperture radar

Among the different types of marine pollution, oil spill has been considered as a major threat to the sea ecosystems. The source of the oil pollution can be located on the mainland or directly at sea. The sources of oil pollution at sea are discharges coming from ships, offshore platforms or natural seepage from sea bed. Oil pollution from sea-based sources can be accidental or deliberate. Different sensors to detect and monitor oil spills could be onboard vessels, aircraft, or satellites. Vessels equipped with specialised radars, can detect oil at sea but they can cover a very limited area. One of the established ways to monitor sea-based oil pollution is the use of satellites equipped with Synthetic Aperture Radar (SAR).The aim of the work presented in this thesis is to identify optimum set of feature extracted parameters and implement methods at various stages for oil spill detection from Synthetic Aperture Radar (SAR) imagery. More than 200 images of ERS-2, ENVSAT and RADARSAT 2 SAR sensor have been used to assess proposed feature vector for oil spill detection methodology, which involves three stages: segmentation for dark spot detection, feature extraction and classification of feature vector. Unfortunately oil spill is not only the phenomenon that can create a dark spot in SAR imagery. There are several others meteorological and oceanographic and wind induced phenomena which may lead to a dark spot in SAR imagery. Therefore, these dark objects also appear similar to the dark spot due to oil spill and are called as look-alikes. These look-alikes thus cause difficulty in detecting oil spill spots as their primary characteristic similar to oil spill spots. To get over this difficulty, feature extraction becomes important; a stage which may involve selection of appropriate feature extraction parameters. The main objective of this dissertation is to identify the optimum feature vector in order to segregate oil spill and ‘look-alike’ spots. A total of 44 Feature extracted parameters have been studied. For segmentation, four methods; based on edge detection, adaptive theresholding, artificial neural network (ANN) segmentation and the other on contrast split segmentation have been implemented. Spot features are extracted from both the dark spots themselves and their surroundings. Classification stage was performed using two different classification techniques, first one is based on ANN and the other based on a two-stage processing that combines classification tree analysis and fuzzy logic. A modified feature vector, including both new and improved features, is suggested for better description of different types of dark spots. An ANN classifier using full spectrum of feature parameters has also been developed and evaluated. The implemented methodology appears promising in detecting dark spots and discriminating oil spills from look-alikes and processing time is well below any operational service requirements

On Small Satellites for Oceanography: A Survey

The recent explosive growth of small satellite operations driven primarily from an academic or pedagogical need, has demonstrated the viability of commercial-off-the-shelf technologies in space. They have also leveraged and shown the need for development of compatible sensors primarily aimed for Earth observation tasks including monitoring terrestrial domains, communications and engineering tests. However, one domain that these platforms have not yet made substantial inroads into, is in the ocean sciences. Remote sensing has long been within the repertoire of tools for oceanographers to study dynamic large scale physical phenomena, such as gyres and fronts, bio-geochemical process transport, primary productivity and process studies in the coastal ocean. We argue that the time has come for micro and nano satellites (with mass smaller than 100 kg and 2 to 3 year development times) designed, built, tested and flown by academic departments, for coordinated observations with robotic assets in situ. We do so primarily by surveying SmallSat missions oriented towards ocean observations in the recent past, and in doing so, we update the current knowledge about what is feasible in the rapidly evolving field of platforms and sensors for this domain. We conclude by proposing a set of candidate ocean observing missions with an emphasis on radar-based observations, with a focus on Synthetic Aperture Radar.Comment: 63 pages, 4 figures, 8 table

SIGNAL: A Ka-band Digital Beam-Forming SAR System Concept to Monitor Topography Variations of Ice Caps and Glaciers

This paper discusses the implementation of an endto- 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

A novel satellite mission concept for upper air water vapour, aerosol and cloud observations using integrated path differential absorption LiDAR limb sounding

We propose a new satellite mission to deliver high quality measurements of upper air water vapour. The concept centres around a LiDAR in limb sounding by occultation geometry, designed to operate as a very long path system for differential absorption measurements. We present a preliminary performance analysis with a system sized to send 75 mJ pulses at 25 Hz at four wavelengths close to 935 nm, to up to 5 microsatellites in a counter-rotating orbit, carrying retroreflectors characterized by a reflected beam divergence of roughly twice the emitted laser beam divergence of 15 µrad. This provides water vapour profiles with a vertical sampling of 110 m; preliminary calculations suggest that the system could detect concentrations of less than 5 ppm. A secondary payload of a fairly conventional medium resolution multispectral radiometer allows wide-swath cloud and aerosol imaging. The total weight and power of the system are estimated at 3 tons and 2,700 W respectively. This novel concept presents significant challenges, including the performance of the lasers in space, the tracking between the main spacecraft and the retroreflectors, the refractive effects of turbulence, and the design of the telescopes to achieve a high signal-to-noise ratio for the high precision measurements. The mission concept was conceived at the Alpbach Summer School 2010

IMPROVING AND EXPANDING PRECISION ORBIT DERIVED ATMOSPHERIC DENSITIES

Atmospheric drag is the most uncertain non-conservative force acting on a low Earth orbiting satellite. The existing atmospheric density models are not accurate enough to model the variations in density, which significantly affect the drag on satellites since drag is directly proportional to atmospheric density. In this research, precision orbit ephemerides (POE) are used as measurements in an optimal orbit determination scheme to estimate corrections to baseline atmospheric density models. These corrections improve the drag estimates, which in turn improve orbit determination and prediction and also provide a better understanding of the upper atmosphere. The POE are used as measurements in a sequential measurement and filtering scheme using the Orbit Determination Tool Kit (ODTK) software, which provides the orbit determination. Five atmospheric density models are available in ODTK, which are used as baseline atmospheric density models to which corrections are made in the orbit determination. These density models are Jacchia 1971, Jacchia-Roberts, CIRA 1972, MSISE 1990, and NRLMSISE 2000. The user has the option to specify the ballistic coefficient (BC) correlated half-life and density correlated half-life. These half-lives are usually given values of 1.8, 18, or 180 minutes. If all five baseline density models are used along with three different combinations of ballistic coefficient and density correlated half-lives, then this would result in forty-five different cases. All the forty-five cases are examined in some studies and only a selected few are examined in others, the details of which are given in the appropriate sections. The POE derived densities are validated by comparing them with accelerometer derived densities for satellites which have accelerometers onboard, such as the Challenging Minisatellite Payload (CHAMP) and the Gravity Recovery and Climate Experiment (GRACE). The trend in the variation is compared quantitatively by calculating the cross correlation between the POE and accelerometer derived densities, and the magnitude is compared by calculating the root mean square between the two. The accelerometer derived densities for both CHAMP and GRACE are available from Sean Bruinsma of CNES and also from Eric Sutton of the United States Air Force Research Laboratory, and are used in this research. The effect of different functions of geomagnetic planetary amplitude (ap) as an input in orbit determination to estimate atmospheric density was investigated. The three different functions of input are 3-hourly ap step functions, linear interpolated ap functions, and ap osculating spline functions. These three different types of functions were used as inputs for all the forty-five different combinations obtained by using the five different baseline atmospheric density models and three different combinations of ballistic coefficient and density correlated half-lives as stated earlier, and POE derived density was estimated for both CHAMP and GRACE. The POE derived densities were compared with the accelerometer derived densities by calculating the CC and RMS. To create continuous data sets of POE derived densities that span a period of one week, the linear weighted blending technique was used to blend the 14 hour POE derived densities in their overlap periods. CIRA 1972 was used as the baseline atmospheric density model and a BC correlated half-life of 1.8 minutes and density correlated half-life of 180 minutes were used as inputs in ODTK to generate these POE derived density estimates. These one week continuous POE derived densities showed better correlation with accelerometer derived densities than HASDM densities for both CHAMP and GRACE. The average cross-sectional area of the satellite that is normal to the velocity vector, the area facing the Sun, and the area facing the Earth, were determined so that these areas could be used to estimate the atmospheric drag, the force due to solar radiation pressure, and the force due to Earth radiation pressure (infrared and Earth albedo). This was done for both TerraSAR-X and ICESat. For TerraSAR-X, the area normal to the velocity vector was assumed be a constant and equal to the frontal area, and the area facing the Earth was also assumed to be constant. However, the area facing the Sun varied with time. The average area facing the Sun for a period of 14 hours and also the annual average area were calculated and used to calculate the POE derived densities. The POE derived densities calculated using these two different average areas facing the Sun were found to be very similar. Since TerraSAR-X does not have an accelerometer onboard, the POE derived densities could not be compared with accelerometer derived densities, but instead were compared with Jacchia-71 densities since this was also one of the outputs from ODTK. The POE derived densities were also compared with NRLMSISE 2000 densities. The attitude of ICESat as a function of beta angle was given in the literature and so was the average area of each side of the satellite when it was modeled as a rectangular box with two solar panels. This information was used to estimate the 30-hour average area normal to the velocity vector, area facing the Earth, and area facing the Sun, for ICESat. The POE derived densities using these areas were estimated by ODTK and compared with the Jacchai-71 density model

Potential of Spaceborne X & L-Band SAR-Data for Soil Moisture Mapping Using GIS and its Application to Hydrological Modelling: the Example of Gottleuba Catchment, Saxony / Germany

Hydrological modelling is a powerful tool for hydrologists and engineers involved in the planning and development of integrated approach for the management of water resources. With the recent advent of computational power and the growing availability of spatial data, RS and GIS technologies can augment to a great extent the conventional methods used in rainfall runoff studies; it is possible to accurately describe watershed characteristics in particularly when determining runoff response to rainfall input. The main objective of this study is to apply the potential of spaceborne SAR data for soil moisture retrieval in order to improve the spatial input parameters required for hydrological modelling. For the spatial database creation, high resolution 2 m aerial laser scanning Digital Terrain Model (DTM), soil map, and landuse map were used. Rainfall records were transformed into a runoff through hydrological parameterisation of the watershed and the river network using HEC-HMS software for rainfall runoff simulation. The Soil Conservation Services Curve Number (SCS-CN) and Soil Moisture Accounting (SMA) loss methods were selected to calculate the infiltration losses. In microwave remote sensing, the study of how the microwave interacts with the earth terrain has always been interesting in interpreting the satellite SAR images. In this research soil moisture was derived from two different types of Spaceborne SAR data; TerraSAR-X and ALOS PALSAR (L band). The developed integrated hydrological model was applied to the test site of the Gottleuba Catchment area which covers approximately 400 sqkm, located south of Pirna (Saxony, Germany). To validate the model historical precipitation data of the past ten years were performed. The validated model was further optimized using the extracted soil moisture from SAR data. The simulation results showed a reasonable match between the simulated and the observed hydrographs. Quantitatively the study concluded that based on SAR data, the model could be used as an expeditious tool of soil moisture mapping which required for hydrological modelling