Alaska High Altitude Photography (AHAP)

[mbjones]

• Alaska High Altitude Photography (AHAP)
• Arc ImageServer: https://nrcsgeoservices.sc.egov.usda.gov/arcgis/rest/services/ortho_imagery/ahap/ImageServer
• WMS capabilities doc: https://nrcsgeoservices.sc.egov.usda.gov/arcgis/services/ortho_imagery/ahap/ImageServer/WMSServer?request=GetCapabilities&service=WMS

Thumbnail of coverage:

From Hig:

I recently became aware of a GIS REST server for orthorectified AHAP imagery - the AK false-color infrared images collected in the late 70s to mid 80s. These are fantastic images, and very useful for various purposes. I was just using it to tell which rock glaciers were active.

The data is available here:

https://nrcsgeoservices.sc.egov.usda.gov/arcgis/rest/services/ortho_imagery/ahap/ImageServer

It says this was produced by the USDA FPAC BC GEO BRANCH from USGS scans. I have no idea who organized this effort. The only contact info I've come across is through the "report service errors" link, which provides this email address: usdafpacbc@servicenowservices.com.

This nrcsgeoservices source works but is fantastically slow. If I use it, I have to turn the layer on then go do something else for several minutes.

It seems like this would be a high-value data layer within PDG / ADC. Would it be in-scope for you guys to find a way to acquire and host the data on a more usable platform?

[mbjones]

I also found this page, which indicates this was a long running federal program, and it seems like the data are in the public domain. There also may be a copy at USGS too.

https://www.alaskamapped.org/docs/ahap/

The copy at the PGC is described here, and fully downloadable: https://www.pgc.umn.edu/data/aerial/. So I am not sure this should be a high priority for us. We could discuss with PGC whether it would make sense to tile the data for better use in interactive maps -- they currently have a map server showing flightline trajectories, which covers more of the state than the USDA service seems to:

[mbjones]

Reading further on the PGC page, they say:

The imagery is not accurately placed nor orthorectified. Errors can be up to 500 meters.

But the metadata from the USDA copy indicated an extensive rectification process took place, and they say their copy has much lower error in the abstract:

The output orthomosaic tiles are rendered as a target resolution of 1.5 meter GSD and are delivered in a Decimal Degrees, Spheroid-WGS 1984, Datum-WGS 1984 projection for which the majority of the cell footprint falls. Horizontal accuracy of 10 meters at 95% confidence in lower elevation areas with cultural landmarks (urban areas) and 20 meters confidence in Glaciers/Mountains.

So it looks like the USDA copy has some additional valuable processing. @clairecporter might have thoughts on this data.

[clairecporter]

PGC serves up the ungeoreferenced versions of these photos through our app. We used to have a roughly geo-reffed version as well. We are actually in the midst of rebuilding that. This USDA product is way higher quality, though, and we'd be happy to serve it, either as individual downloadable files or as a web service, as long as the USDA project agrees.