Many topographic scenes exhibit complex dynamic behavior that is difficult to map, quantify, predict and understand. A terrestrial laser scanner fixed on a permanent position can be used to monitor such scenes in an automated way with centimeter to decimeter quality at ranges of up to several kilometers. Laser scanners are active sensors, and are therefore able to continue operation during night. Their independence from texture conditions ensures that in principle they provide stable range measurements for varying surface conditions. Recent years have seen a strong increase in the employment of such systems for different scientific applications in geosciences, environmental and ecological sciences, including forestry, glaciology, and geomorphology. At the same time, this employment resulted in a new type of 4D topographic data sets (3D point clouds + time) with a significant temporal dimension, as systems are now able to acquire thousands of consecutive epochs in a row. Extracting information from these 4D data sets turns out to be challenging, first, because of insufficient knowledge on error budget and correlations, and, second, because of lack of algorithms, benchmarks, and best-practice workflows. This paper provides an overview of different 4D systems for near-continuous laser scanning, and discusses systematic challenges including instability of the sensor system, meteorological and atmospheric influences, and data alignment, before discussing recently developed methods and scientific software for extracting and parameterizing changes from 4D topographic data sets, in connection to the different applications.

Vietnam's promising economic growth has led to energy shortage, growing coal imports, and increasing carbon emissions. The country's electricity demand annual growth rate has been 12% in recent years and is projected to be 8–9% by 2030. In Vietnam 40% of the land is dedicated to agriculture and thousands of inland water bodies are used for agriculture/aquaculture. Utilising even a small portion of them for Floating Photovoltaics (FPVs) would mitigate land-use conflicts and benefits agriculture and aquaculture. To demonstrate FPVs' potential, we selected a hydropower dam reservoir in the North and six irrigation reservoirs in the South. System Advisor Model (SAM) software was used to simulate the electricity generated if we cover 1%, 5%, and 10% of surfaces of these reservoirs. The results show a potential capacity close to 1 GWp and annual potential generation of 1.4 TWh if 1% of these surfaces were covered by FPVs. We also evaluated FPVs potential for four different types of water bodies in Vietnam: Lake, Lagoon, River and Without Classification. The results showed that the potential capacity, considering use of only of 1% of these water surfaces for FPVs is 3.7 GWp, and provides 5385 GWh generation, which highlights the significant contribution that FPVs can make to the renewable energy sector in this country. However, FPVs face some socio-technical barriers, including regulatory ambiguity about water rights, uncertainty about economic policies and limited information about their environmental impacts that could hamper the expansion of this technology, and need to be addressed through further research.