TanDEM-X Interferometry for Mangrove Height Estimation and Change Detection

By Raimon Bach Pareja

Abstract
Mangroves play a key role in climate change mitigation due to their ability to sequester carbon. The global mangrove extent has been on an ongoing declining the past decades, which makes the monitoring of this unique ecosystem crucial. The purpose of this thesis was to assess the suitability of TanDEM-X (TDM) data and the Two-Level Model (TLM) to map mangrove height and change in Komo-Mondah, Gabon. There was an emphasis on comparing height estimates between phase height and TLM height, as well as on analysing height change patterns. The main data consisted of 10 TDM acquisitions (5 from 2011-2012 and 5 from 2022) and LiDAR RH metrics (LVIS & GEDI). First, data indicates that high coherence can be observed for the majority of mangroves in the study area, which together with other factors could hint stable phase estimates. Second, it is argued that the TLM does not provide better height estimates than phase height, partly because of a lack of an extensive DTM. The phase height was, however, highly biased. Especially for acquisitions with mangroves exceeding the height of ambiguity (HOA). Already processed TDM phase data proved to provide much better height estimates, which was assumed to be a result of a more advanced processing chain that included HOA maps. Third, the findings suggest that in general, there has been rather limited height change in the study area between 2011 and 2022. One specific region (East of Libreville) was found to consistently show a strong decrease among all estimates, which was also confirmed by literature.