icess(n)

ICESS PROGRAM OUTPUT

The ICESS program fits a plane to a block of data from the Airborne

Topographic Mapper (ATM) which has been processed to the stage in which

each data point has a surface elevation (ellipsoid height) and a

geographic location (latitude and east longitude). As commonly

utilized, the data on the two sides of the aircraft are separately

smoothed. The alongtrack distance smoothed is the distance which the

aircraft moves in 0.5 seconds. The data output rate is 4/second so that

there is 50% overlap between successively smoothed blocks. The program

output is an ASCII file. The date of the data is contained in the first

6 characters of the file name. Each data record contains the following

ten words:

Word 1: Time at which the aircraft passed the mid-point of the block

(in seconds of the day)

Word 2: Latitude of the center of the block in degrees

Word 3: East longitude of the center of the block in degrees

Word 4: Ellipsoid height (WGS84 ellipsoid) of the center of the block

Word 5: South to North slope of the block (dimensionless)

Word 6: West to East slope of the block (dimensionless)

Word 7: RMS fit of the ATM data to the plane (in centimeters)

Word 8: Number of points used in estimating the plane parameters

Word 9: Number of points edited in estimating the plane parameters

Word 10: Distance of the center of the block from the centerline of the

aircraft trajectory (in meters)

Note: The two "slopes" estimated are used to estimate surface

elevations at points other than the center point through the use

of the following algorithm:

ht(phi,lambda) = ht(phi0,lambda0)

+ SNslope * (phi - phi0) * 6378137 * pi/180

+ WEslope * (lambda - lambda0) * cos(phi0) * 6378137 * pi/180

where the center coordinates of the block are (phi0,lambda0)

ICESSN

ICESSN PROGRAM OUTPUT

The Airborne Topographic Mapper (ATM) measures a sequence of points

scanned in a swath along the aircraft flight track. Each ATM point

has a surface elevation (ellipsoid height) and a geographic location

(latitude and east longitude). The ICESSN program condenses the ATM

measurements by fitting a plane to blocks of points selected at regular

intervals along track and several across track. The block size and spacing

can be specified, but a few typical values are used. The alongtrack

distance smoothed is the distance which the aircraft moves in a fixed

interval (0.5 seconds for P-3 aircraft, 1.0 seconds for DHC-6 twin-otter).

The data output interval is half of the smoothing interval so that there

is 50% overlap between successively smoothed blocks. For each along-track

position/time, there are multiple blocks spaced evenly across-track to span

the swath width. Typically the number of blocks is 5 for the 22-degree

off-nadir scanner (T3), 3 for the 15-degree off-nadir scanner (T2), and

2 for the 10-degree off-nadir scanner flown in 1993. There is an additional

block located at aircraft nadir with a width typically set to 80m. If a

single profile is desired, the nadir profile can be selected from the full

data set. The program output is an ASCII file.

The date of the data is contained in the first 6 characters of the

file name (YYMMDD), and the start time in the following 6 digits (HHMMSS).

Each data record contains the following eleven words: