For almost two years, satellite navigation has been used in reconnaissance exploration. However, only in the last six months has it been demonstrated that an “integrated” system provides navigational accuracy for all geophysical prospecting. This paper describes the accuracy of the integrated system and illustrates its merits. The primary objective of the integrated system is to provide continuous, accurate, geodetic position information. This is accomplished by integrating instantaneous position, velocity and heading from outputs of the Doppler sonar, gyrocompass, velocimeter, vertical references with periodic updates obtained from the Navy Navigation Satellite System. Each of the subsystems, their operations and functions will be discussed. Satellite navigation offers many advantages for marine surveys. Features for point‐to‐point automatic steering, onboard plotting of shotpoint data, firing of seismic energy source as a function of exact distance and real‐time data logging onto digital tape have been implemented. With the onboard computer all navigation, gravity and magnetic information is recorded on tape and some preprocessing and filtering of gravity and magnetic data may be accomplished.

The Piggy-Back Marine Exploration System consists of an instrumented shallow draught barge mounted on a boat or mother ship. In this manner both shallow water and deep marine operations can be efficiently performed. For shallow water operations the vessels are separated, the mother ship acting in the role of a logisti cs and support base, the barge bei ng the work boat.Aboard the ship is a computer-controlled, integrated navigation and digital data acquisition system. Navigational elements include a satell ite receiver, Doppler sonar and heading reference for deep water operation. When operating with the barge in shallow waters (J.! -45' depths), a shorebased radio positioning system is employed and ground control is establ ished with the satellite receiver system. All geophysical and navigation data is digitally recorded and the operation provides the capabil ity to acquire gravity and magnetic data as well as the seismic refraction and reflection data. Under computer control either both vessels or the barge alone (in shallow water operations) make good a prespecified course, the sequencing of the seismic system being automatically triggered at uniform distances along the survey line.Operational advantages of the Piggy-Back systemReferences and illustrations at end of paper.are illustrated and many of the features mentioned are shown under actual field conditions. The economics and efficiencies of the Piggy-Back system more than justify its claim to being a versatile full capability marine exploration system.

Over the past four years, integrated satellite navigation systems have found increasing use on offshore geophysical survey vessels. A need has arisen for additional knowledge of the accuracy limitations of these systems.

Data reduction of navigation parameters recorded in real-time is a key phase of satellite navigation in marine geophysical operations. The positioning system operates in a statistical predictor-corrector manner and is complemented by post processing of the shipboard data to provide the most precise postplots. INTRODUCTION Integrated satellite navigation systems are a valuable tool in today's marine exploration efforts. Such systems have proven accuracy and reliability in real-time. However, because of larger statistical data sets, that is, data before and after any given position, the post survey data reduction can further enhance the overall accuracy. Data reduction compensates 'for systematic errors and smoothes the "saw tooth effect" (see Figure 1) of real-time statistical filtering (i.e., Kalman, minimum variance, least squares, etc.). To perform the reduction task the following steps (see Figure 2) are required:Edit field dataAnalyze and recompute satellite fixesDetermine and remove systematic errorsAdjust random errorsCompute and plot auxiliary dataPlot preliminary mapsCheck and adjust mistiesPlot final maps BASIC PHILOSOPHY The basic function of the integrated satellite navigation system is to control the position of the vessel on a preplanned course or "line" during the geophysical survey (see Figure 3). Most operations are defined as "on-line" or "off-line." While "on-line" the integrated navigation system serves as a shot point counter, i.e., it determines the "on-line" course and transmits a discrete pulse, on the basis of distance traveled, to the geophysical recording system which performs the data acquisition and recording operations. The integrated system, while computing position and maintaining vessel course, records positional information on digital magnetic tape. Computations are based on inputs to a digital computer froma satellite receiver,a Doppler sonar,a gyrocompass,an inelinometer, anda velocimeter (see Figure 4). These inputs are sampled continuously to determine the vessel's position at one-half second intervals. Onboard data is filtered in a predictor-corrector (Kalman) manner to obtain optimum real-time results. It is this data recorded on magnetic tape and its post processing that is the subject of the discussion below. SATELLITE FIX COMPUTATION To compute optimum post survey positions, all navigation data, that is, satellite message data and other sensor information are recorded on magnetic tape. The first step is to edit the field reel verifying all recorded data and checking for data "drop out" (missing data, gaps in recording, loss due to parity errors) and to merge auxiliary data from external navigation aids. The most reliable data obtained by integrated satellite navigation systems are satellite fixes. Although fixes are not absolutely correct, in a stationary position accuracies of 150 feet RMS may be expected (see Table 1).