GLAS – Spaceborne LiDAR

IceSAT was a unique satellite launched in 2003 with the aim to provide accurate topographic information of the Earth’s surface over a number of years. One of it’s aims was recovery of ice sheet mass balance and cloud property information, as detailed on NASA’s page here. Onboard this satellite was an instrument called GLAS, the geoscience laser altimetry system, a spaceborne LiDAR I’ve been meaning to look at for a long time. Last Sunday I decided to give it a look in the afternoon, and after a bit of tinkering with the files available here I produced a point cloud showing the Earth’s topography as seen by GLAS, collated for one month in 2003.

The files are structured that topographic information (The GLAH14 and GLAH15 files I used) are split up for each individual day, each with 14 orbits per file. I’ve presented one of the files below, as seen in CloudCompare, about 1.3 million points.

GLAS_One

GLAH14 data collected on the 4th March 2003

As you can see, each day doesn’t recover a detailed scan of the Earth, so a collation of the month gives us a better idea as to the extent of the mission.

GLAS_March

GLAH14/15 data for all of March 2003 – ~64,000,000 points

I really like this as not only can you see the completeness of the data (I had to mask lots of points), but it gives you a really good idea of what a low earth orbit looks like. IceSAT orbited about 600km above the Earth’s surface, and this is the pattern produced.

After removing duplicate points we can then compare each of the heights recovered from each laser pulse. For practicality’s sake I just used height above the WGS84 ellipsoid, a term different from height above sea level which is normally used. This which just saved a bit of time, one of a couple of other corners which were cut to produce the cloud. This gives us a global model of surface topography for March 2003, shown below.

GLAS_Ref

The final product is pretty interesting and it was a really fun exercise to do. I’m hosting the model on my webspace also, which is viewable here.

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