USGS AERIAL IMAGE CAPTURED FROM AN INTERACTIVE MAP SERVER AT CITY OF BERKELEY

This aerial photo image is actually a composite of a digital terrain model hillshade under a slightly transparent orthophoto.
The orthorectified aerial photograph was produced for the U.S. National Geospatial Intelligence Agency, to specifications
prepared by the U.S. Geological Survey.  This survey's natural color image sample interval is 30cm on the ground.

This area of central Marin county, California was flown 20031021 from about 40,000 feet elevation. Imagery were captured by a
Leica Geosystems ADS-40 airborne digital scanner. The ADS-40 uses a pushbroom scanning approach as used by certain commercial
imaging satellites: both forward-angled and aft-angled panchromatic scans are made along with a four-band nadir-directed image scan.
All scans are oriented abeam the aircraft.

Fore- and aft-scan images correlate for a stereo phtogrammetric-derived digital surface model (DSM) generated as a continuous track.
The DSM from this survey posts elevation values every 2 meters on a grid covering the entire imaged ground surface, and is produced
by an ADS-40 processing-capable package called ISTAR.  After the DSM is created, its surface was used when to adjust pixel positions
along image tracks collected at nadir to build an orthorectified natural color image. It is worth noting that  ADS-40 nadir scan has
parallax only abeam, and so more of the gathered imagery has perspective nearly above the subject than obtainable with focal-plane
style imaging surveys flown at lower elevations with large-format film and also with focal plane digital cameras.  

The resulting ISTAR-processed image has three bands; here the bands are visible red, green, and blue for natural color.
In more agricultural areas it is often desirable to use near infrared, visible red, and green--printed respectively as red,
green, and blue. In such images vigorous plants appear red. 

The image presented here is a screen shot thumbnail from an map viewer published by City of Berkeley, California USA at
http://map.ci.berkeley.ca.us/jspviewer and that server is loaded with over 300 GB of orthorectified imagery.  This sort of
imagery is useful for spatial analysis because of its true scale and ability to overlay many non-image map features.  One
example is shown where Corte Madera creek, in the right part of the image, and Phoenix lake, in the left part of the image
are tinted with ligther blue polygons.  These polygons are a local view of a statewide seamless coastal water and lake layer
for California that has been aggregated from 1;24,000 mapping and includes inland waters gathered from The National Map at
http://nationalmap.gov as published during June 2005.

The City of Berkeley-published map viewer allows browsing through a seamless interface, panning and zooming into areas of
interest, and turning various map layers visible or not as desired.  Browsability is a valuable part of interactive mapping, and
this image is simply a screen shot from one moment in a long browsing session that explored undeveloped areas of Marin county.

Long description written by Brian B. Quinn - version 20060513