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Multi-temporal analysis of canopy surface heights has high potential for a forest monitoring system. TanDEM-X interferometric synthetic aperture radar (InSAR) heights provide a global data source for a multi-temporal height analysis as two global coverages from the global digital elevation model (DEM) phase 2010–2014 and the Change DEM phase 2017–2020 exist. However, the potential of estimating small scale and subtle changes with TanDEM-X heights is to date underexplored. The detection of subtle changes was assessed in this study. Penetration depth estimations were applied as a first step in a framework to avoid pseudo-changes based on errors and different acquisition properties. The results suggest that subtle changes are detectable, but an improved error assessment is necessary in order to provide a detection with high accuracy.

With the global TanDEM-X DEM generation being finished in 2016, the mission is now acquiring a new dataset to provide an independent DEM, the so-called "TanDEM-X Change DEM". It is based on a completely new dataset acquired from 2017 – 2019 in contrast to the acquisitions for the global DEM between 2010 and 2015 in the aim to characterise terrain changes. It benefits from improvements in the acquisition planning process and in the data processing which enable to achieve reliable DEM data of high accuracy with fewer acquisitions. For this goal, the use of an edited TanDEM-X DEM as "starting point" for the processing is mandatory. Detectable 3d elevation changes are presented exemplarily in Indonesian forest and on an outlet glacier in Antarctica.

Since 2010, TanDEM-X and its twin satellite TerraSAR-X fly in a close orbit formation and form a single-pass synthetic aperture radar (SAR) interferometer. The formation was established to acquire a global high-precision digital elevation model (DEM) using SAR interferometry (InSAR). In order to achieve the required height accuracy of the TanDEM-X DEM, at least two global coverages have to be acquired. However, in difficult and mountainous terrain, up to five coverages are present. Here, acquisitions from ascending and descending orbits are needed to fill gaps and to overcome geometric limitations. Therefore, a strategy to properly combine the available height estimates is mandatory. The objective of this paper is the presentation of the operational TanDEM-X DEM mosaicking approach. In general, multiple InSAR DEM heights are combined by means of a weighted average with the height error as weight. Apart from this widely used mosaicking approach, one big challenge remains with the handling of larger height discrepancies between the input data, which are mainly caused by phase unwrapping errors, but also by temporal changes between acquisitions. In the case of inconsistencies, the TanDEM-X mosaicking approach performs a grouping into height levels. A priority concept is set up to evaluate the different groups of heights considering the number of DEMs and several InSAR quality parameters: the height error, the phase unwrapping method, and the height of ambiguity. This allows the identification of the most reliable height level for mosaicking. This fusion concept is verified on different test areas affected by phase unwrapping errors in flat and mountainous terrain as well as by height discrepancies in forests. The results show that the quality of the final TanDEM-X DEM mosaic benefits a lot from this mosaicking approach.

Ongoing global warming causes dramatic changes globally, especially with respect to Polar Regions. In this context, digital elevation data is of high importance for most glaciological applications. In this paper, we investigate TanDEM-X penetration depth over snow and ice on the Greenland ice sheet. In particular, the relation of backscatter intensity and interferometric coherence to penetration depth of the X-band InSAR signal is explored in order to improve the reliability of TanDEM-X elevation data. The analyses showed a distinct relationship of backscatter intensity, coherence and penetration depth. In addition, the influence of the height of ambiguity of the interferometric TanDEM-X data is presented. On an experimental test site in Northern Greenland, we demonstrated the estimation of TanDEM-X penetration depth based on backscatter intensity and interferometric coherence utilizing a linear regression model.

The digital elevation model (DEM) produced by TanDEM-X is an interferometric elevation model with global unprecedented quality, accuracy, and coverage. It represents an unedited surface model that means for example in case of water bodies it still contains noisy, random or void DEM values. For the most applications a DEM editing is crucial. After all, as every application has its own requirements in this paper we describe a framework especially developed for TanDEM-X DEM to automatically edit the DEM according to specific user requirements. Originally, the tools were developed for editing SRTM X-Band DEM. Currently this framework is extended within the RASOR project (Rapid Analysis and Spatialisation Of Risk) towards a specific editing to support multi-hazard risk assessment but also for general editing purposes.

TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurements) is an Earth observation radar mission that consists of a SAR interferometer built by two almost identical satellites flying in close formation [1]-[4]. With a typical separation between the satellites of 120 to 500 m a global Digital Elevation Model (DEM) with 2 m relative height accuracy at 12 m posting is being generated. While the main mission phase for DEM data acquisition has been finished in 2014, the processing of the global TanDEM-X DEM will be concluded mid-2016. Final DEMs for more than 65% of all land masses are already available for scientific and commercial applications. A 15-month science phase of the TanDEM-X mission started in October 2014 which offers the opportunity to explore the generation of DEMs with even higher accuracy for selected areas, and to demonstrate the capabilities of this unique mission for new scientific applications.

In September 2013 the production of TanDEM-X digital elevation model (DEM) started. As the data acquisition for difficult terrain lasted until April 2014, final DEM production started for flat to moderate terrain regions where two final coverages surfice. This paper focuses on a first validation of moderate terrain to prove the absolute height accuracy. In a detailed comparison three DEM tiles from different continents are chosen to validate the TanDEM-X DEM by computing differences to GPS tracks, ICESat validation points, and SRTM. On a global scale all TanDEM-X DEMs produced so far are compared with ICESat and GPS tracks. Both validations presented here for the first time indicate that the absolute height error for moderate terrain for TanDEM-X is below 2m and therefore much better than the specified 10m/LE90.

For the global TanDEM-X DEM the whole world will be acquired by at least two coverages. Thereby on the one hand phase unwrapping errors are reduced by applying the dual-baseline method and on the other hand a low noise level is ensured even for difficult areas like forests and steep terrain. During DEM mosaicking, the single interferometric DEMs are merged together. This paper focuses on the combination of heights in overlapping areas with significant height differences. The challenge here is to choose the most reliable height value. The improvement applying this strategy in contrast to simple averaging and the general benefit of using more than one acquisition is shown by means of some example mosaics.

The aimed accuracies for the final TanDEM-X DEM of 10m absolute and 2m relative height error will be ensured by calibration data. One crucial data set for the relative accuracy is tie-points that connect adjacent DEM acquisitions in the approximately 4km-overlap-area with each other. In this paper an improved concept for tie-point candidates is presented that is based on averaging a larger region instead of comparing single points. This concept should be more robust against noise. It is validated by applying the DEM calibration on a simulated test area, as real TanDEM-X data was not yet available. Also, the DEM calibration will be validated for the first time on a larger “real” test site by applying the TanDEM-X processing scenario.

The TanDEM-X mission will derive a global digital elevation model (DEM) with satellite SAR interferometry. Height references play an important role to ensure the required height accuracy of 10m absolute and 2m relative for 90% of the data. In this paper the main height reference data sets ICESat (for DEM calibration), SRTM (for phase unwrapping) and kinematic GPS-Tracks (KGPS – for DEM verification) are analyzed regarding to their accuracy. For the ICESat data a reliable quality measure is developed. For SRTM an improved version adjusted to reliable ICESat data is presented and a concept for collecting and evaluating decimeter-precise kinematic GPS tracks is proposed.

The TanDEM-X mission will derive a global digital elevation model (DEM) with satellite SAR interferometry. The aimed accuracies are an absolute height error of 10 m and a relative height error of 2 m for 90% of the data. This requires a correction of the elevation heights after interferometric processing by residual systematic DEM errors. The estimation and correction of these errors is called DEM calibration. This paper gives an overview of the DEM calibration strategy within the TanDEM-X mission. First, the error sources and their influence on the DEM are determined by a functional description. Then, a strategy for a new block adjustment of DEMs is set up and evaluated with simulated and real DEMs.

Summary form only given. The German Aerospace Center (DLR) has developed the TerraSAR-X Ground Segment. One part is the geocoding system that provides orthorectification capability for multi- resolution, multi-polarisation and multi-frequency data. Besides an ellipsoid corrected product a new product called Enhanced Ellipsoid Corrected (EEC) will be offered that considers digital elevation models (DEM) of a moderately coarser resolution then the 1 up to 3 m resolution of the TerraSAR-X modes. SRTM/X-band DEMs with approximately 25 m spacing will be the backbone for this operational and fully automated service. As optional product an geocoded incidence angle mask (GIM) is available providing information about the incidence angle of the radar beam, as well as about layover and shadow areas. High precision terrain correction using high resolution DEMs, tie-pointing and image adjustment will be implemented in an experimental processor. This paper gives detailed information on the image quality, which is examined in detail based on the first available geocoded TerraSAR-X products. Therefore radiometric and geometric aspects will be investigated. It is to be shown that the orthorectification step does not tamper the original radiometric properties. The geometric accuracy of the orthorectification mainly depends on the quality of the used DEM. Besides the SRTM/X-band DEM additional elevation data like SRTM/C-band, ERS-derived and GLOBE data are used for EEC generation. The achieved pixel location accuracies will be presented. The quality characteristics of the Geocoded Incidence Angle Mask - depending also on the used DEM - are described. Moreover the high precision orthorectified image (called geocoded terrain corrected - GTC) will be examined with regard to pixel location accuracy. A high resolution laserscanning DEM, tie-points and image adjustment will be used for this analysis. Furthermore information regarding processing performance will be given.

The German Aerospace Center (DLR) currently develops the TerraSAR-X Payload Ground Segment. On request level lb products will be distributed to the user. Two of the four basic products available are generated by the geocoding system. This system supports ellipsoid and terrain correction in order to provide orthorectified images. A new product called Enhanced Ellipsoid Corrected (EEC) will be offered that considers Digital Elevation Models (DEMs) of a moderately coarser resolution than the resolution of the TerraSAR-X modes. SRTM/X-band DEMs with approximately 25 m resolution will be the backbone for this operational and fully automated service. For high precision terrain correction first results of an experimental processor are presented using a high resolution DEM, tie- pointing and image adjustment.