Table of Contents - The Atmospheric Studies Group at TRC

Section 2: Geophysical Data Processors
Table 2-2 (continued)
Sample TERREL Control File Inputs
(TERREL.INP)
TERREL constructs gridded terrain elevations (m MSL), and may also
estimate the terrain elevation at discrete points by selecting the
peak elevation within a prescribed distance (km) from each point.
When processing discrete points, the XYINP.DAT provides the grid
coordinates (km) of each point, and may also include a height above
ground (m) for each point (e.g. for elevated receptors). The
structure of the XYINP.DAT file is a free-format text file with
either 2 columns (X,Y) or 4 columns (X,Y,Elevation,Height). When
the 4-column form is used, data in the 3rd column are replaced
with the elevations obtained from the terrain data base files.
Report elevations for discrete (X,Y) points
(LXY) Default: F ! LXY = F !
T = Yes (XYINP.DAT and XYOUT.DAT files are used)
F = No (XYINP.DAT and XYOUT.DAT files are NOT used)
Interpolate elevations for discrete points
(Used only if LXY=T)
(LINTXY) Default: F ! LINTXY = T !
T = Yes (elevations will be interpolated)
F = No (elevations will be terrain peaks)
Number of data columns in XYINP.DAT file
(Used only if LXY=T)
(NXYCOL) Default: 4 ! NXYCOL = 2 !
Search radius (km) about each (X,Y) for locating terrain peak
or for carrying out interpolation
(Used only if LXY=T)
(XYRADKM) No Default ! XYRADKM = 0.15 !
Some terrain data sets contain void areas where the data are
missing. Others may contain areas where data are inaccurate (noisy).
Both situations occur mostly over oceans or large lakes, but for SRTM
data it can also occur over land due to the data set still evolving.
These void (missing) or noisy input data can be replaced in several
ways.
Noisy Data ---
Noise affects SRTM data for oceans and lakes and the adjacent shores,
due to the scattering effects of water on radar measurements.
The most obvious occurence of noise is negative elevations for water
and adjacent land points. This can be filtered with the specification
of a minimum acceptable elevation by water/land type. Extracted
elevations that are greater than this minimum are retained, while those
lower than this minimum value can be re-defined as missing for
subsequent treatment by the missing values processing, or can be
replaced with either the minimum value or with another default value
defined for treatment of void (missing) data. The minimum values must
be chosen judiciously for the region being treated since some regions
have valid elevations below MSL.
Missing data ---
Cells with missing elevations can be interpolated from surrounding
cells with valid values, and a maximum search radius is defined.
Also, if coastline processing has been used, default elevations for
each water/land type can be defined and used in place of voids.
This replacement can be carried out as the final step before output
on a cell-by-cell and receptor-by-receptor basis, or can be carried
out for values extracted from the terrain files as missing. This
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