Digital elevation modeling through forests: the challenge of the Amazon

Abstract

Elevation mapping at ground level is challenging in forested areas like the Amazon region, which is mostly covered by dense rainforest. The most common techniques, i.e. photogrammetry and short wavelength radar, provide elevations at canopy level at best, while most applications require ground elevations. Even lidar and P-band radar, which can penetrate foliage and measure elevations at ground level, have some limitations which are analyzed in here. We address three research questions: To what extent can a terrain model be replaced by a more easily available canopy-level surface model for topography-based applications? How can the elevation be obtained at ground level through forest? Can a priori knowledge of general continental relief properties be used to compensate for the limits of measurement methods in the presence of forest?

Latest Trends in Modelling Forest Ecosystems: New Approaches or Just New Methods?

“…As in the case of other disturbances, abiotic factors such as slope, elevation, distance to roads, or weather patterns are important for incorporating complexity at small spatial and temporal scales [73]. However, getting good quality for such small-scale variables could be a challenge in areas with dense forest cover and sparse road networks, as is the case in most tropical or boreal forests [74].…”

“…This approach aims to bring nonacademic forest stakeholders into the process at the beginning, so they develop a sense of ownership of the research outcome and therefore are much more likely to implement the model outcomes. Three models for sciencepolicy interaction have identified [74]: the "linear phase" when science informed policy-making in a unidirectional manner, the "interactive phase" when both sides found themselves in a continuous interaction, and the "embedded phase." Our own experience is that the linear phase is still dominant in many regions, with scientists developing models and scenarios of their interest and then approaching nonacademic stakeholders with their results.…”

Multicriteria Evaluation of the Potential of P-Band Airborne Radar Dems for 3d Characterisation of Hydrography in Tropical Forests

“…In the case of tropical forest regions, such as the Amazon, these requirements are more difficult to meet. Indeed, in addition to difficult field access and to the cloud cover, the presence of forests, with an average height of about 30 m and a very irregular texture, makes it impossible to observe the ground with optical techniques (such as photogrammetry) and even with short wavelength radar interferometry (Polidori et al 2022). Therefore, those methods provide a model of the canopy elevation, which turns very uncertain the description of hydrography due to important elevation and slope errors, especially in areas with moderate relief.…”

Comparação entre os Modelos Digitais de Terreno gerados por Radar em Banda P e LiDAR na Amazônia, um estudo de caso no Amapá (Brasil).

“…Os sensores mais utilizados para a extração de Modelos Digitais de Elevação (MDE) usam um comprimento de onda curto, são sensíveis ao dossel e não ao terreno, semelhantes nesse sentido à Fotogrametria. Segundo Polidori et al (2022), o grande problema desses dados é que a maioria dos MDT são, na verdade, MDS (Modelo Digital de Superfície, que se trata da representação dos dosséis em aglomerados de árvores) e, na maioria das aplicações desses modelos, os autores os utilizam como se fossem MDT.…”