Single-pass Interferometric SAR satellite configurations offer unique opportunities for observing dynamic features of ice masses. Future cross-track interferometry constellations of satellite missions will produce interferometric DEMs over virtually all glaciers globally and will offer significant advancements for regular monitoring their surface elevation. In the present contribution we want to address some of the main issues encountered when mapping the topographic changes with multitemporal TanDEM-X InSAR DEMs over glaciers. We illustrate open questions for InSAR DEM data acquisition when targeting height change rate calculation for mountain and outlet glaciers at large scale.

The TanDEM-X mission acquires data used for the generation of Digital Elevation Models (DEMs) since 2010. From this data two global DEMs are already generated or in generation. The DEM acquisitions used for new TanDEM-X DEM 2020 are also used to generate TanDEM-X DEM Change Maps. Furthermore, the DEM Change Maps can be combined with the additional TanDEM-X DEM datasets and used for the generation of TanDEM-X DEM Change Map Stacks. This paper presents these new products on the basis of an example of an open-pit mining area in Australia. Additionally, the potentials and challenges of the DEM Change Map stacks are presented.

The Earth is a very dynamic system and the topographic height of its landmass changes over time, especially in forested areas, glaciers, permafrost regions or where human activities take place. After the TanDEM-X mission provided a first global DEM of unprecedented quality in 2016, a new complete coverage of the Earth's landmass was acquired mainly between 2017 and 2020. This data is used to create another global DEM. In addition to providing more up-to-date elevation information, these new acquisitions also provide a great dataset to show the changes that have occurred in the few years between the two global datasets. The new product - the TanDEM-X DEM Change Maps - will be produced in 30m and 90m postings and will focus on showing these changes between the first global TanDEM-X DEM and the newly acquired time-tagged DEM scenes. It will also include the in-house automatically edited TanDEM-X DEM.

The TanDEM-X mission has acquired multiple global coverages of data over the last years in order to create digital elevation models (DEMs). The data between 2017 and 2020 is processed to Change RawDEMs (CRaw DEMs). These scenes are successfully pre-calibrated individually during the processing. However, in order to determine and quantify terrain changes between the new data and the former global TanDEM-X DEM, the calibration can be improved even further. In the case of large-scale terrain changes like glaciers or forestation areas CRaw DEMs might be calibrated on the change instead of the smaller stable regions. A comparison of to the calibration of neighboring scenes gives information on which scene has to be corrected. This paper summarizes the pre-calibration during the processing of the CRaw DEMs and analyzes the results of the calibration and corresponding change detection. Furthermore, a method for a post-calibration of the CRaw DEMs is presented. This method will be used to create TanDEM-X DEM Change Maps in the future.

In 2017, the TanDEM-X Mission decided to generate a second - more recent - global DEM. The acquisitions took place from 2017 till mid 2020 and represent a new global coverage of the whole Earth's landmass. This global dataset is well separated in time from the data used for the first global TanDEM-X DEM. Recent terrain height information can be delivered globally again with similar accuracy and consequently, terrain changes can be monitored. Currently, this data is being processed by the Integrated TanDEM-X Processor (ITP) into pre-calibrated single scenes. A reference DEM is a pre-requisite to enable a correct interferometric processing.

Over the last years the TanDEM-X mission acquired data for a second global digital elevation model (DEM) the TanDEM-X Change DEM. This new DEM is temporally independent of the former global TanDEM-X DEM and therefore yields the possibility of change detection. In order to decrease the phase noise level the interferometric processing for the Change DEM has been upgraded. This also allows a more accurate change detection. Currently, the processing of the global data is performed operationally. It includes the detection of terrain changes and first examples of detected terrain changes can be presented.

The “TanDEM-X Change DEM” will be a new DEM consisting of the data globally acquired by the TanDEM-X mission from 2017 until 2020. This new DEM aims to characterize terrain changes which occurred between the acquisition of the TanDEM-X global DEM, acquired between 2010 and 2015, and the new temporally independent and up-to-date data set. The new data will mostly contain only one global coverage. Therefore, necessary improvements in the acquisition planning process as well as in the interferometric processing were made. Specifically, a new adaptive filtering approach is presented in this paper as well as its influence on the interferometric phase and the DEM for test sites over Germany and Chile.

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.