Data Acquisition
The Leica ADS40 Airborne Digital Sensor was used for 100% of
the data acquisition. The ADS40 delivered all digital data for the state. The sensor's
construction allows for the simultaneous acquisition of seven bands of
information. The ADS40 is a “push broom” style line-scanner that captures
pictures along a scan line looking forwards, downwards and backwards from
the aircraft.
The ADS40 simultaneously captured black and white, natural color, and color-
Infrared data. It produced high-quality digital surface models with reduced
ground control requirements, and with coregistration
of all the data sets. For more information see acquisition vendor EarthData and
Leica.
Coverage included the entire state of Indiana (36,602 square miles, more or less) with a 1,000-
foot buffer outside the state boundary. Along rivers separating the Illinois and Kentucky
borders, the buffer was 1,000 feet or to the opposite bank, whichever distance was greater. Data were
acquired during leaf-off conditions, snow-free, with less than 5% cloud cover. Adjacent flight
lines overlapped by a minimum of 30 percent. The imagery was acquired with 60 to 80% side-lap
over downtown areas in Indianapolis and Fort Wayne in order to produce “true” orthoimagery in
which building lean was been eliminated.
A combination of targeted and photo-identifiable ground control and airborne GPS (AGPS) were used to acquire
controlled imagery. Nearly 500 control targets were used to support the aerial photography mission. All ground
control were tied to the Indiana High Accuracy Reference Network
(HARN) and were established by surveyors
licensed in the State of Indiana.
Project survey crews can survey 50-quality assurance/quality control (QA/QC) checkpoints dispersed throughout
the state. These points were used for QA/QC of the aerial triangulation and orthorectification. These
station locations were provided to photogrammetrists who located them from the photography and
compared them with the GPS derived locations. Project survey crews also surveyed an additional 100 photo-identifiable
QA/QC blind check points dispersed throughout the state that were provided
to the State for external QA/QC. All control data and information were provided as part of the final deliverable
products.
Indiana received Federal Geographic Data Committee (FGDC) standard metadata, including a separate metadata
file for each individual county coverage. The FGDC
specification used was Content Standard for Digital Geospatial Metadata Version 2 (FGDC-STD-001-1998).