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SRTM Data Editing Rules
(Version 2.0, March 12, 2003)
1. Purpose
The purpose of this document is to define in detail specific SRTM DTED
2 finishing requirements originally outlined in the SRTM Prototype Processing
Statement of Work. This document has been compiled from a combination of
NIMA and OMNIBUS sources and has been refined and updated through the
course of the SRTM Prototype Development period.
2. SRTM Data Processing Methodologies
2.1. Water Processing
2.1.1. Conformance to DTED Specification. SRTM DTED 2 water
processing requirements are derived from the DTED Performance
Specification MIL-PRF 89020B. It is the intent of NIMA to produce
SRTM-derived DTED 2 which conforms as closely as possible to these
requirements given SRTM and ancillary source capabilities and SRTM
DTED 2 post-processing throughput requirements.
2.1.2. Government Furnished Information (GFI). In addition to the SRTM
products, NIMA will make available additional products to assist with the
water processing effort. This Government Furnished Information (GFI)
includes water mask information derived from Landsat source
(LANDCOVER). The LANDCOVER data have been transformed into a
geographic projection and formatted into one degree by one degree cell
size areas (ERDAS format). The LANDCOVER data are of similar
resolution to DTED 2, however there are currency issues relating to the
age of the Landsat source (up to 10 years older than SRTM data) and
horizontal registration (approximately 50 m horizontal accuracy vs. 20 m
for SRTM) with respect to the SRTM data. In certain areas of a cell
where the OIM solution is indeterminate (sandy areas in dry
environments, frozen lakes and/or snow cover, or discrepancies between
OIMs), Landcover may be the best alternative for delineation provided
that there seems to be good congruence between the Landcover and
OIMs where both are available in other areas of the cell. CADRG will
also be available as ancillary data sources, however given the nature of
the various sources and differences in water body and island size
portrayal requirements between the various CADRG products, these
may be of limited usefulness. CADRG is never to be used for
delineation of features. In all cases, SRTM elevation data needs to
logically support extraction/placement of features.
Version 2.0, March 12, 2003

22.1.3. Non-GFI Sources and Consistency. Sources other than NIMA-
provided GFI is NOT to be used for SRTM DTED 2 finishing. The
rationale for this rule is NIMA’s goal of worldwide data consistency for
this data set. For several reasons consistency is likely to decline if
referral to non-GFI sources is permitted. One of these is that the
availability and reliability of these sources may vary widely, especially
from continent to continent. Additionally, there is no way to document
the use of these sources. One of NIMA’s primary goals is to try to
produce data with as much consistency as possible, whether that be
from cell to cell or continent to continent. Early in the project it was
decided not to try to produce a gold-plated version of one continent -
which may then not be consistent with the rest of the global data set.
2.1.4. Flexible Processes. During the course of the SRTM Prototype
Development, NIMA contractors have developed water-processing
capabilities that utilize various combinations of SRTM and GFI sources.
It should be noted that there will likely be cases when ancillary GFI is not
available for a variety of reasons. This scenario should drive
development of flexible processes that do not rely too heavily on any one
source. Assessment of the various general finishing scenarios will be
addressed in Section 3.6 of this document.
2.2. THED Processing
SRTM Terrain Height Error Data (THED) will be modified and
updated per instructions contained in the SRTM Data Product
Specification. Additional case-specific guidance is outlined in Section 5
of this document.
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3. Water Editing Conventions
1. DTED Specification and Practical Implementation. Specific water
processing requirements have been taken from the DTED 2 specification
MIL-PRF 89020B and are excerpted at the beginning of each section
below. This is followed by a more detailed production implementation
definition. The intent is to provide sufficient information for production
prototype algorithm development. These definitions will form the basis
for SRTM DTED 2 water processing requirements. It is anticipated that
values for some parameters may be revised as the prototyping
progresses or as production requirements dictate. All horizontal
measurement requirements are listed below in meters, however the
actual requirements shall be based on the approximation that each
DTED-2 post is 30 m x 30 m.
2. Editing of Excessive Automatic Feature Classification Detail.
Excessive detail generated by automatic feature classification processes
Version 2.0, March 12, 2003