We often work with our fix wing drones (e-bee) in very dense tropical forest areas between 200 ha and 5000 ha. We fly at 100-120m high and have an Overlap of 80%-85% and 70% Sidelap. We need the altitude curves between 25-50cm equidistance (hydrology projects). What represents the DTM and the resulting curves, the tree crowns or the ground? We work with at least 5 GCP and 3 Checkpoints. But often we have so dense forests, where the camera (Canon PS110, Canon SX260, Sony WX500 und Sequoia) does not look at the ground. The questions: If we only have closed forest and the forests are hilly or in the mountains, and the GCP can only be placed at the edge zones of the forests, what represents the DTM.
If the same situation is flat forests, what represents the DTM. If the forest has a “hole” where the GCPs are placed, what does the DTM represent? Or in other Words, is the DTM consistent in all three situations? How would you obtain consistent data of elevation working with drones in dense tropical forest.
What do you recommend for these situations in order to obtain consistent high-altitude data.
Then the final question: If we compare the DSM with the DTM in these situations, can we derive the tree height from it?