An Unbiased Analysis of the Doppler Coordinate Systems,
DEFENSE MAPPING AGENCY HYDROGRAPHIC/ TOPOGRAPHIC CENTER WASHINGTON DC ADVANCED TECHNOLOGY DIV
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The Doppler system has undergone at least five major revisions, or improvements, in its definition since original inception. Some of the so-called minor modifications of the past have not been well documented and corresponding rigorous updating of the software in many instances is also lacking. The actual impact and contribution of each such modification and the absence of proper updating towards inner consistency are not negligible in the present sub-meter era. The questions whether 1 the Broadcast Ephermeris BE based coordinates are either automatically calculated in the WGS 72 datum or derived with respect to the reference ellipsoid for the WGS 72 datum 2 the BE system, except for a small bias, is close to the NSWC 9Z-2 system 3 the BE based coordinates are in the NWL 9D system or strictly speaking in the modified NWL 10D system 4 the Doppler coordinate system as NWL 9D prior to June 1977 and is NSWC 9Z-2 now and 5 the coordinate system NWL 9D andor NSWC 9Z-2 is geocentric or has a significant Z-axis bias, are still floating around. The net result is misunderstanding and misinterpretation for many users. The present paper tries to highlight some of the related problems and to answer them as well as possible.