645 



If the Geosat GM data were declassified, die ERS- 1 and Geosat 

 data could be combined to improve the resolving power slightly 

 beyond the capabilities of either data set alone. Declassification 

 of Geosat GM data would be particularly beneficial in the 

 equatorial regions, for several reasons. First, the ground track 

 spacing of the orbits is largest at the equator, and hence the 

 resolving power of the data sets is least. Second, the ERS-1 

 orbit is more polar than Geosat, so that at the equator ERS- 1 is 

 not expected to resolve the east component of gravity as well as 

 the north component of gravity. Third, there are a number of 

 important outstanding scientific problems in this area. 



In addition to the value of Geosat data for inferring marine 

 gravity fields, the Geosat GM data are important in studying 

 global change. The GM data were acquired during an important 

 time in the El Nirio cycle. The release of the GM data would 

 extend the range of time available for studying the seasonal and 

 interannual sea-level changes and allow better calibration of 

 long-range forecastmg models. The release of the raw GM data 

 would allow the calculations of sea level change between GM 

 and ERS-1 or Topex/Poseidon. 



d. Findings 



The findings relative to Geosat Altimetiy are: 



• It is evident that there will be significant improventents in the 

 accuracy and resolution of the marine gravity field north of 

 30^ if Gecsat classified high-track-density data become 

 available. Such availability would support a variety of 

 geo<l3'naniic ^plications. 



• The availability of the Geosat data will extend the range of 

 time available for studying sea level changes that are possibly 



^associated wifli the B Nino cycle. 



SBfeJ 

 4. SEAFLUOR SEDIMENT PROPERTIES 



a. Data Description 



The academic community does not have a complete, 

 comprehensive, digital database of sediment thickness and 

 sediment type. The Navy has developed such a database and 

 has incorporated it in a sea-fioor acoustic reflection loss model, 

 Low Frequency Bottom Loss (LFBL). The global sediment 



properties database has been derived from a variety of classified 

 and unclassified sources, including open ocean survey operations 

 and seafloor measurements (cores and reflection profiling) 

 taken in shallow waters around the worid, as well as use of 

 coring data from the Deep Sea Drilling Project (DSDP), the 

 International Program of Ocean Drilling, and the Ocean Drilling 

 Program. In addition, the Navy has databases containing a 

 variety of information about sediment subsurface structures 

 (e.g., salt domes) that are also unique. 



Figures 10 and 11, taken together, present both global scale 

 (Figure 10) and regional scale (Figure 11) representations of 

 surface sediment type and sediment thickness on the seafloor. 

 These figures illustrate the quality and coverage of some of the 

 data types currently available in the Navy's unique global 

 seafloor sediment properties database. 



b. Accessibility 



The LFBL acoustic reflection loss model, which was the 

 Navy's rationale for developing the sediments database, is 

 actually composed of two distinct parts: a database of geo- 

 physical and acoustic parameters over seafloor regions, and an 

 acoustic model, which calculates acoustic bottom loss for 

 selected frequencies across a full range of acoustic grazing 

 angles. The data in the first LFBL construction were derived 

 fi'om unclassified sources. Further refinement and data additions 

 by NAVOCEANO led to the classification of the LFBL. 

 MEDEA's major interest is in the sediment thickness and 

 sediment type sub-files. Although unclassified, the LFBL 

 sediment thickness and sediment type files have not been 

 distributed outside the Navy's oceanographic/acoustic 

 community. 



The Navy also maintains a Geological Laboratory database of 

 site specific bottom cores and grab samples. This database has 

 both restricted and classified content. 



c. Scientific Utility 



The release and unrestricted distribution of the sediment 

 databases, including the thickness and sediment type parts of 

 LFBL and other databases containing information about 

 subsurface structures, would provide the academic community 



17 



