LIDAR

Light detection and ranging  Produces high resolution, accurate elevation information

collection  Airborne laser (can also be a ground system.)  Shoot out laser beams, measure return time. If you know the position of the airplane very accurately, the angle at which you are shooting the beam, and the return time, you can get a distance.  Which is then converted to an elevation  Up to 150,000 pulses per second. Makes for a very data rich environment.  Uses visible – NIR light.

On plane  Very accurate GPS  Gyroscopes and accelerometer – records roll, pitch, and yaw.  Laser beam.  Return reflection instrument.  A computer which can then convert all this into point elevations.  Again, dealing with millions of points.

 Laser scans back and forth  The faster the laser and the closer to the ground, the better the resolution  Can be tricky, as you can get multiple returns from individual laser pulses – in vegetation!

End product: a point cloud.  A ton of points floating in space. Tagged as first through ?? returns.  Obviously, the intensity of the returns will diminish with the number of returns.  Typically, a LAS file.

So.. Talk about these returns  First return. Top of canopy (in vegetated areas)  Last return – should be ground level.  Lots of applications in veg mapping! (some of you may have seen the talk last quarter?)  And… much editing required, though automated tools get better and better.

Berkeley

OK. We have points. What now?  Typically, want first or last returns, unless really looking at canopy.  So.. Filter your dataset to get what you want  Now, build an elevation model. Either a TIN or a DEM.  Which you can bring into a GIS for analysis, etc.

 I’ve seen these detailed enough to pick out fenceposts – and even fence and power lines.

Applications  DEMs  Veg mapping  Looking through canopy  Archaeology!  Also, just looking at minute changes in elevation and such.

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