| Columbia River, WA/OR (P260) Bathymetric Digital Elevation Model (30 meter resolution)
Derived From Source Hydrographic Survey Soundings Collected by NOAA |
| Bathymetry for the Columbia River was derived from forty-five surveys containing 306,711
soundings. Nine older, overlapping, less accurate surveys were omitted before tinning
and the overlap from three older, less accurate surveys was omitted. The average separation
between soundings was 45 meters. The surveys used dated from 1935 to 1958. The range
of soundings for the forty-five surveys was 3.0 meters to -59.1 meters at mean low
water. Mean high water values between 0.1 and 2.0 meters were assigned to the shoreline.
Forty-one points were found that were not consistent with the surrounding points.
These were removed prior to tinning. DEM grid values outside the shoreline (on land)
were assigned null values (-32676). The Columbia River has thirty-three 7.5 minute
DEMs and four one degree DEMs. The 1 degree DEMs were generated from the higher resolution
7.5 minute DEMs which covered the estuary. A Digital Elevation Model (DEM) contains
a series of elevations ordered from south to north with the order of the columns from
west to east. The DEM is formatted as one ASCII header record (A- record), followed
by a series of profile records (B- records) each of which include a short B-record
header followed by a series of ASCII integer elevations (typically in units of 1 centimeter)
per each profile. The last physical record of the DEM is an accuracy record (C-record).
The 7.5-minute DEM (30- by 30-m data spacing) is cast on the Universal Transverse
Mercator (UTM) projection. It provides coverage in 7.5- by 7.5-minute blocks. Each
product provides the same coverage as a standard USGS 7.5-minute quadrangle but the
DEM contains over edge data. Coverage is available for many estuaries of the contiguous
United States but is not complete. |
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