How accurate are satellite images?

Amped SRL recently announced an update to Authenticate which includes an integration with SunCalc.org. It's a pretty cool free on-line tool to check for sun positioning relative to time and place. Kudos to Amped for adding the integration and speeding up the workflow for this task.

The discussion of this new integration on Amped's blog notes that this integration can be used to check theories of the case relative to statements made and either supported or refuted by images taken of the scene.

As a technical investigator and analyst, this is a cool new integration that speeds up what many were doing anyway - including myself occasionally.

An important caveat about SunCalc.org is necessary, however. They utilize ESRI maps when showing the satellite view overlay (ESRI Satellite).

Available Base Maps at SunCalc.org 

Ordinarily, this wouldn't be a problem. However, if you head over to the ESRI web site and ask the question, how frequently are the world imagery base maps updated, you might be surprised at the answer.

Answer:

"The World Imagery basemap is not collectively updated. Rather, on occasion, updates occur on the different images within the basemap, and there is no actual known cycle for this activity. 

The basemap is made up of several imagery tiles. In ArcMap, the Identify tool can be used to find out the date when a specific tile of interest was updated. 

Additional information is available in the Related Information section below, including metadata for the basemap and a list of all Community Maps Program contributors."

Yes, in ArcMap, you can use the Identify tool to determine the age of the tile. But, you're not using ArcMap, you're using SunCalc. There's really no way within the SunCalc interface to determine the age of the tile you happen to be viewing.

As a way of illustrating the point, this view contains a feature on the property of interest that hasn't been physically present for some time. Thus, this image tile is at least several months old. With this in mind, you'll want to be extremely careful in making judgements about the scene when using SunCalc.

Don't get me wrong. I like SunCalc. But, in the fast-changing western US, one has to be sure that the features in question are actually present in the view seen on SunCalc's page.

Have a good day, my friends.