The great-circle subroutines are based upon a sphere 

 21,600 nm in diameter and can have a maximum error of 20 nm 

 over a distance of 1 hemisphere (about 11,000 nm) . This 

 amounts to an error of about 2nm/l,000nm of range. For 

 profiles of 1,000 nm or less this error is insignificant in 

 propagation model applications, but it could be important at 

 very long ranges. The magnitude of this error depends upon 

 the difference in shape between the sphere and the oblate 

 spheroid and on the method of path generation. Greater accuracy 

 can be obtained by using a geodesic v/here the error is 1 m in 

 latitude, longitude, and range and 0.035 sec. in bearing within 

 a hemisphere (Thomas, 1965 and 1970). 



Within each MSQLOC area there is a difference between the 

 path followed by the great circle and the actual path along which 

 the depths values are interpolated (fig. 18) . Because SYNBAPSl 

 requires a straight line along which to interpolate depth values, 

 a rhumb line between the first position entering a 5-degree square 

 and the last position before leaving the square is used instead 

 of the curved great-circle path. For all great circles that 

 follow a meridian or the equator this difference is zero. For 

 all other directions, the maximum difference is located at the 

 approximate mid-point along a rhumb line within 5-degree square. 

 Under the most unfavorable condition of high latitude and an 

 east-west orientation, this difference rarely exceeds 2 nm. 



Preliminary estimates of the accuracy of the interpolated 

 depth values in the profile plane are + 15 fm. This assumes that 

 there are no positional errors in the great-circle path in the 

 horizontal plane. A completed data bank, including regions of 

 smooth to rough topography, will be needed before full error 

 analysis can be undertaken. 



C. Status Program 



Program SYNSTAT queries the random-access storage device 

 through the SYNTABLE for a listing of the identification group 

 from each MSQLOC gridded data block. This listing includes the 

 file key as in the following example: 



DATE ADDED TO 

 RANDOM-ACCESS 

 DEVICE 



18 April 1972 



19 April 1972 



All MSQLOC gridded data blocks or selected ones can be listed. 

 They are selectable through SYNSTAT control cards as shown in 

 figure 19. 









ACTUAL 









FILE 



RELATIVE 



BLOCK 



NO. OF 



NO. OF 



MSQLOC 



KEY 



ADDRESS 



SIZE 



COLUMNS 



ROWS 



1. 1291 



E08C 



50176 



4704 



63 



74 



2. 1292 



E08C 



54880 



4704 



63 



74 



32 



