The main goal of the TerraSAR-X Add-On for Digital Elevation Measurements (TanDEM-X) mission is the generation of a global digital elevation model (DEM) of unprecedented accuracy and coverage. The global TanDEM-X DEM product became available in 2016, surpassed all expectations, and became a reference for a wide range of Earth science, commercial, and geospatial applications. In addition, new information products, such as DEM change maps (DCMs), have been developed and are available to the geoscience and remote sensing community. Beyond the operational products, new science applications have been demonstrated and are summarized in this article, along with experimental data acquisitions. This article also aims to provide an overview of science activities with TanDEM-X data and science data acquisitions planned for the coming years.

This paper proposes the wrapped staring spotlight (WSS) SAR imaging mode, which is a new method to extend the azimuth steering capability for phased array SAR to achieve either an improved azimuth geometric or radiometric resolution. It investigates the utility of steering directions with main lobe gains that are smaller than that of the grating lobes and exposes how these directions can be exploited. Furthermore, two methods are proposed to reduce the speckle and the image noise at once, i.e., the Look-Normalized Pattern Correction and the Ω-weighting. Based on two example TerraSAR-X WSS acquisitions, the image performance of extended and point targets is discussed.

The paper proposes wrapped staring spotlight SAR, a method to extend the azimuth steering capability for phased array SAR systems. Based on two TerraSAR-X (TSX) wrapped staring spotlight example acquisitions, the image performance of point and extended and targets is discussed. In the provided examples, the steering is extended until the gain of the grating lobes becomes much stronger than the gain into steering direction. By this, it becomes possible to improve the azimuth resolution by a factor of two when compared to that of the starring spotlight mode implemented in the operational TSX processing chain.

The paper reports about a basic analysis of a distributed SAR system realized by several small satellites. The potential for Pulse Repetition Frequency (PRF) reduction and the corresponding swath width extension is discussed. It is derived how to maintain a gap-free phase center (PC) sequence while increasing the inter-satellite distance. The paper presents different kinds of configurations. The one that solves the problem combines alternating transmit (tx) and dispersed receive (rx) satellites. An example configuration suitable for ship monitoring is established. It serves to illustrate the problem statement and its solving.

This contribution presents two experiments performed with the TerraSAR-X (TSX) and TanDEM-X (TDX) satellites working in the pursuit monostatic configuration. Their objective is to estimate the along-track component of the motion in the scene in repeat-pass scenarios with an accuracy better than the one given by the stripmap azimuth resolution. Such performance is possible by exploiting the angular diversity of the bidirectional (BiDi) SAR mode and the π-shifted (or staggered) TOPS.

This paper discusses observations of the ocean surface using a combination of along-track SAR interferometry and the recently proposed Bidirectional SAR acquisition mode. The paper discusses the expected performance, and shows first experimental results with TanDEM-X acquisitions.