Monday, October 6, 2014

Daily Dose of MODIS

I've written previously about the MODIS satellites and their constant imaging of the planet; CalTopo's fire activity layer is derived from their infrared sensors, with a lot of post-processing by the federal government.  There's now a new pair of layers that make use of the visible-spectrum sensors: current and archived MODIS imagery.


The Latest MODIS layer can be found under the Aerial Imagery group.  Imagery is acquired twice a day, but note that the first pass may not happen until the afternoon.

All quiet in California, but a little foggy on the coast.

The layer has a nominal resolution of 250 meters / pixel, but since the imagery is often not tack sharp, usable resolution will be less:

Not quite enough to read license plates.

The latest image may be covered with clouds, or the area you're interested in may be especially blurry if it was at the edge of an imaging strip.  That's where the archived imagery comes in, as a new configurable layer option:


Choose which pass you want (the satellites are named Aqua and Terra), the date you want imagery from - today, yesterday, or any day back to May 2012 - and you're off and running.


You may be thinking "so this is a fun toy, but how does such a low resolution image help with backcountry trip planning?"  To answer that question, lets dial the clock back a couple weeks to September 16, when the King Fire was going strong:


CalTopo's fire activity layer pulls in smoke polygons from a separate source, but there's nothing like seeing it with your own eyes.

As another exercise, a light storm blew through the Sierra shortly before some friends headed to Desolation Wilderness last fall.  They asked me how much snow to expect, and I erroneously under guessed as Truckee had already melted out several days prior.  If only they'd had easy access to MODIS imagery, it would have been obvious that their destination was still coated in a thin layer of the white stuff.  As an added bonus, you can make out smoke plumes from controlled burns along the western slope of the Sierra:


This has barely gone live and I'm already in the habit of checking it once a day, just to see if anything interesting is going on.