24th February 2009, 03:28 PM
Actually, lidar can't exactly see through trees.
You can remove the trees in post processing if you have suitable data. The first return bounces off the canopy, and the last return pulse can penetrate to the forest floor. You can take the last return data points and interpolate a digital terrain model. This only works if you fly the lidar at the right time of year, in winter. Otherwise, you get no pulses bouncing back off the forest floor, and the first and last return data look much the same. If I sound a bit narked, it is because this is what i'm looking at now, prehistoric field systems disappearing under tree cover....
Even with good high res data, some trees are more easily filtered out then others. Holly is a dense bugger, and usually leaves a mound in the data. However, this can be useful as a reference point, given that holly is not common in most woodland.
In answer to Plautus, the technology allows the large cave of data to be much more freely available then before. Lots of digs don't really add masses of useful data, but there are plenty of larger scale projects which can all contribute to the picture...
You can remove the trees in post processing if you have suitable data. The first return bounces off the canopy, and the last return pulse can penetrate to the forest floor. You can take the last return data points and interpolate a digital terrain model. This only works if you fly the lidar at the right time of year, in winter. Otherwise, you get no pulses bouncing back off the forest floor, and the first and last return data look much the same. If I sound a bit narked, it is because this is what i'm looking at now, prehistoric field systems disappearing under tree cover....
Even with good high res data, some trees are more easily filtered out then others. Holly is a dense bugger, and usually leaves a mound in the data. However, this can be useful as a reference point, given that holly is not common in most woodland.
In answer to Plautus, the technology allows the large cave of data to be much more freely available then before. Lots of digs don't really add masses of useful data, but there are plenty of larger scale projects which can all contribute to the picture...