METHOD AND APPARATUS FOR MULTI-LINE SEISMIC EXPLORATION

Abstract: A multi-line seismic survey system including a plurality of geophone arrays on each line. Each geophone array is individually addressable by a central control unit. Addressing of the individual geophone arrays is accomplished by means of a reference system. This reference system also facilitates the monitoring of shotpoint location in reference to the multi-line system and further facilitates the accessing of individual geophone arrays in response to the seismic shotpoint.

Description: METHOD AND APPARATUS FOR MULTI-LINE SEISMIC EXPLORATION BACKGROUND OF THE INVENTION This invention relates generally to methods and apparatus for seismic exploration and more particularly relates to methods and apparatus for three-dimensional seismic exploration- Conventional seismic exploration systems typically utilize "lines" of sensor groups, each sensor group composed of one or more individual sensors or geophones, utilized to obtain seismic data. Often each sensor group will include from 1-30 geophones electrically intercon¬ nected to form a single data channel. Conventional systems utilize a multi-conductor seismic cable containing many conductor pairs, one pair for each sensor group, to transmit the seismic data from the sensor groups to a central processor including multi-channel data processing and recording capability. In seismic exploration it is often desirable to utilize a plurality of these lines of sensor groups so as to receive the effects of an energy source at variously- spaced locations relative to the location of the energy source. This multi-line operation facilitates three- dimensional mapping of the geological formations being surveyed. Existing techniques for multi-line operation have typically involved setting out a plurality of lines, each line individually coupled to a central control and recording unit (CCU). This requires a large number of cables to be strung out over an, often, large geographical area. This makes not only the initial set up of the seismic survey system very difficult and costly, but also makes any subsequent changes in the physical location of the CCU very difficult. Additionally, such a system requires a great deal of manual operation in order to accomplish various objectives in three-dimensional survey operations, such as shotpoint roll and the associated sensor station roll with accom¬ panying changes in parameters of stations relative to the shotpoint. Further, such systems do not record data in relation to the shot point locations. Shotpoint patterns for such systems are therefore limited by practicalities of shotpoint location monitoring. Accordingly, the present invention provides a method and apparatus for three-dimensional seismic surveying whereby a plurality of lines of sensors may be coupled to a central control and recording unit with a minimum number of cables and whereby data from sensor arrays, and para¬ meters of such data may, be obtained with optimal flexibility and be recorded in relation to individual shotpoint locations. SUMMARY OF THE INVENTION A seismic system in accordance with the present invention includes a ground electronics having a plurality OMP of lines. Each line includes a plurality of geophone arrays arranged at stations along the line. These lines are then coupled back to a CCU which controls data acqui¬ sition from the geophone arrays. In a particularly preferred embodiment, groups of geophone arrays are coupled to control units which serve as interfaces for signal coupling communication between the CCU and the geophone arrays. Also in a particularly preferred embodi¬ ment, each line further includes a signal directing unit which is responsive to the CCU and which may be utilized to regulate the operation of the control units and to receive and process communications between the CCU and the control unit. These signal directing units are preferably coupled together in a serial fashion and may be linked back to CCU by a single link including dual fiberoptic links, each link including two fiberoptic conductor ' s. The seismic survey system of the present invention utilizes a plurality of X-Y coordinates to determine the placement of each active geophone array in the ground electronics. The system may selectively control these geophone arrays and may monitor the shotpoints which produce the seismic energy which is sensed by these arrays through reference inditia which the system establishes and assigns to each signal directing unit, each control unit, and each sensor array. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic illustration of a seismic survey in accordance with the present invention. Figure 1A is an illustration of the CCU shown in Figure 1, depicted in block diagram form. - j E OMPI , y- IPO Figure 2 illustrates a fiberoptic link as utilized with a preferred embodiment of the present invention, depicted in vertical section. Figure 3 illustrates a connector/transceiver as utilized to terminate ends of the fiberoptic link of Figure 3. Figure 4 illustrates the photo detector receiver/amplification circuit of the connector/trans¬ ceiver of Figure 3, depicted in block diagram form. Figure 5 illustrates the optical transmitter of the connector/transceiver of Figure 3, depicted in block diagram form. Figure 6 is a further schematic illustration of both the photo detector receiver/amplifier of Figure 6 and the transmitter of Figure 6. Figure 7 illustrates a remote data acquisition unit suitable for use with the present invention, depicted in three-dimensional view. Figure 8 illustrates the circuitry of the remote data acquisition unit of Figure 7, depicted in block diagram form. Figure 9 illustrates the buzzer alarm logic of Figure 8, depicted in block diagram form. Figures 10 A & B illustrate a single channel of the quad preamp/filter of Figure 8, depicted in block diagram form. Figure 11 illustrates the switch filter control circuit of the circuit of Figure 10. Figure 12 illustrates track a hold, instantaneous floating point and A to D converter circuitry of Figure 8 depicted in block diagram form. Figure 13 illustrates mask control logic included within the timing and control logic circuit of Figure 8. Figure 14 illustrates the timing and control logic of Figure 8, depicted in block diagram form. Figure 15 illustrates box direction/box on line control of Figure 14, depicted in block diagram form. Figures 16 A & B illustrate the Manchester II decoder and serial to parallel converter of Figure 14, depicted in block diagram form and a timing diagram of the operation of such circuit. Figure 17 illustrates box address control circuitry in block diagram form. Figures 18 A & B illustrate EOT detector and EOT generator of the output formater/encoder circuit of Figure 9. Figure 20 illustrates the formater circuit of Figure 8, depicted in block diagram form. Figure 21 illustrates Manchester II coder of Figure 20, depicted in block diagram form. Figure 22 illustrates the function generator of Figure 8, depicted in block diagram form. Figure 23 illustrates the power supply and battery pack of Figure 8, depicted in block diagram form. Figure 24 illustrates a signal directing unit as used in accordance with the present invention, depicted in three-dimensional and in overhead views. Figure 25- illustrates the electronics of the signal directing unit of Figure 24, depicted in block diagram form. Figure 26 illustrates the power supply of Figure 25 in block diagram form. Figure 27 illustrates common circuitry of the multi¬ plex and master control circuit of Figure 25, depicted in block diagram form. Figure 28 illustrates box direction control circuitry of Figure 27, depicted in block diagram form. Figure 29 illustrates the command word/data multi¬ plexer circuit of Figure 27, depicted in greater detail. Figure 30 schematically illustrates command word selector circuitry of Figure 27. Figure 31 illustrates command word decoder circuitry of Figure 27, depicted in block diagram form. Figure 32 illustrates preamble and EOT stripper of Figure 31 in further block diagram form. Figure 33 illustrates Manchester II decoder circuitry of command word decoder of Figure 31, depicted in further block diagram form. Figure 34 illustrates the RTU data encoder of Figures 26 and 27, depicted in block diagram form. Figure 35 illustrates the line steering and EOT regeneration circuitry of the multiplexer and master controller circuitry of Figure 25, depicted in block diagram form. Figure 36 illustrates LO-side RU return data restora- tion circuitry of Figure 25, depicted in block diagram form. Figure 37 illustrates line steering and EOT regenera¬ tion circuitry of Figure 36 in schematic representation. Figure 38 illustrates CW word restoration circuitry of Figure 25, depicted in block diagram form. Figure 39 illustrates a ground electronics grid system including a shotpoint shooting pattern. Figure 40 illustrates the grid system of Figure 38 with a different shooting pattern. Figure 41 illustrates the grid of Figure 39 with a schematic depiction for tapered parameters on the geophone arrays. Figure 42 illustrates a seismic survey system includ- ing both standard and alternate geophone arrays and a schematic representation of their usage in accordance with the present invention. Figure 43 illustrates a flow chart for setting up a system in accordance with the present invention. Figure 44 illustrates a flow chart for establishing operating parameters for a system in accordance with the present invention. Figure 45 illustrates a flow chart indicating one means in accordance with the present invention for incre¬ mentally keeping track of the shot point and data recording channels as the shot point advances. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawings in more detail, and particularly to Figure 1, therein is schematically illus- trated a seismic survey system 10 in accordance with the present invention. Seismic survey system 10 includes CCU 12 which will typically and preferably be located in a truck or similar readily moveable unit. CCU 12 is coupled, preferably by a single fiber optic link 14 to a first recorder takeout unit (RTU) 16A which is then, in a multi-line configuration, serially connected to addi¬ tional, preferably identical, RTU's 16. Each seismic line 20 includes one or more remote data acquisition and control units (RU's) 22 which are prefer¬ ably coupled by fiber optic links to an RTU 16 for that line or to other RU's 22, if multiple RU's 22 are present in the line. These fiber optic links also include a plurality of twisted pair conductors individually coupled to a plurality of takeouts 24 for connecting a plurality of geophone arrays 26. Fiber optic links 14, 19 are terminated at each end by a connector/transceiver 18. Each of these connec- tor/transceivers 18 contains optical receiver and optical _O M transmitter circuitry for appropriately converting signals from electrical to optical or from optical to electrical. Each RU 22 contains the necessary circuitry to preamplify, filter, gain range, and digitize the analog signals from the geophone groups 26. RTU's 16 serve as an interface between lines 20 connected thereto and CCU 12. Each RTU 16 contains circuitry to regenerate the code transmitted between CCU 12 and the RU's 22. Additionally, RTU's 16 facilitate the addressing of any desired line by CCU 12. In general, the operation of a system as depicted in Figure 1 is as follows. Communication from CCU 12 to ground electronics 13, composed of lines 20 with RUs;,22 and RTUs 16 is achieved by use of command words (CWs). The CWs are transmitted continuously and sequentially at a predetermined rate. The CWs provide instruction and sample acquisition commands to the ground electronics. Following each CW is a command called END OF TRANSMISSION (EOT). Ground electronics 13 is divided into two sides, high side 15 (to the right of vertical dotted line 21) and LO side 17 (to the left of the vertical dotted line 21). Each side is commanded simultaneously by CWs communicated across optical link 14 to RTUs 16. Each RU 22 receives and controls signals from a different group 27 of geophone arrays 26 through cables 19. Taking, for example, LO side 17 of ground electronics 13, when RTU 16a receives the CW and EOT, RTU 16a passes the CW on to the next RU, in this case, 22a, and to the next RTU, in this case, 16b. The EOT is similarly passed on to RU 22a, but is blocked from transmission to RTU 16b. OMPI IPO When RU 22a receives the CW, it both passes the CW on to RU 16b, and, acquires a sample on all- channels, each channel assigned to an individual geophone array 26 in group 27. RU 22a receives analog samples from geophone arrays 26 and converts the samples into digital data and stores such data in memory. RU 22b also prepares to receive an EOT and becomes ready to transmit acquired data to CCU 12. When RU 22a receives the EOT, it blocks the EOT from being retransmitted to the next RU, in this example 22d, and begins transmission of the previous acquired sample data to CCU 12. When the transmission of this data is complete, RU 22a will generate an EOT and transmit it to RU 22b. The same process will then be repeated with RU 22b as well as all other RUs on line LO side 17 of line 20a. RTU 16a will independently be monitoring data trans- mitted by RUs 22a, 22b, and any other RUs on LO side 17 of line 20a. When data from these RUs stops, signifying that all data from LO side 17 of line 20a has been transmitted, RTU 16a will transmit a status signal to CCU 12. After the status signal has been transmitted, RTU 16a will generate an EOT and transmit it to RTU 16b which will then pass the EOT on to RU 22c and repeat the same process on line 20b as was carried out on line 20a. This sequence may be repeated through a number of RTUs 16 and RUs 22 over a desired number of lines 20, principally limited only by channel handling capacity of CCU 12 to accommodate data from each sensor station. This same procedure is simultaneously being carried out on the high side of each line by circuitry in the same RTUs 16 and by the associated RUs 22 on high side 15 of ground electronics 13. Referring now to Figure 2, therein is illustrated in vertical section a dual duplex fiber optic link 14 of the type preferably utilized to couple CCU 12 to RTU's 16. It is to be clearly understood that for sake of convenience, all fiber optic links 14, 19 may be of this type, though in the illustrated embodiment, such links will not be utilized to their full capacity or to equal capacities in all placements. Link 14 includes a jacket 32 preferably constructed of polyurethane, which surrounds four optical fibers 34. A buffer tube 35 surrounds each optical fiber 34 to aid in preventing optical fibers 34 from being damaged when they are looped or otherwise bent. A strength member 36 extends through the center of link 14. Strength member 36 may be a Kevlar fiber, an Aramid fiber, a high tensile strength plastic fiber or the like and is provided to relieve tension from the fibers when external forces are applied to the link. Six twisted pairs 38 of wire are also included within link 14 to facilitate usage as link 19 with takeouts for geophone arrays 26 or for use as wirelines for communication equipment. Referring now to Figure 1A, therein is illustrated CCU 12, depicted in block diagram form. CCU 12 contains the necessary equipment to control ground electronics 13 and to receive and retain data therefrom. Those skilled in the art will recognize that the configuration of central control unit 12 may take many forms and that the described embodiment is merely illustrative of one of these forms. Input panel 29 physically couples to connector/transceivers 18 to provide communication between CCU 12 and fiber optic cable 14. Input panel 29 contain signal processing circuitry to reconstitute data received OMPI from ground electronics 13. Input panel also contains decoding circuitry suitable for decoding the encoded data from ground electronics 13 prior to transmitting the data to system controller 31. A similar decoding operation will be discussed in more detail later herein, in relation to operation of the RU's 22. Remote front end (RFE) 33 is a microprocessor-based controller which serves as an interface between ground electronics 13 and system controller 31. RFE 33 includes suitable controls to allow an operator to interface with the system. In a particularly preferred embodiment, the RFE is based upon a Model TMS-9900 microprocessor as manufactured by Texas Instruments Inc. RFE 33 allows the operator to control multi-line operation of seismic exploration system 10, including the selection of operating parameters such as tapered lines (varied gap, preamplifier gain, and geophone source array patterns) as will be discussed in more detail later herein. RFE 33 also contains appropriate circuitry to interface the operations of ground electronics 13 with one or more sources of seismic energy 39. This interface may be accomplished in a generally conventional manner known to the industry. System controller 31 controls the various data manipulation functions -to handle data compilation and retention. System controller 31 also serves as an electronic interface to all peripheral devices, such as mass memory 35, and tape transport 37. System controller 31 is also preferably a microprocessor based system which, at a particularly preferred embodiment, is also based upon the Model TMS-9900 microprocessor manufactured by Texas Instruments Inc. Operator inputs are provided to system controller 31 to allow an operator to issue commands to the peripheral devices attached to the system. For OMP example, associated with system controller 31 in a preferred embodiment is a mass memory 35 has a capacity of 3.9 megawords. More than one mass memory may be utilized to facilitate the recording in a greater number of data channels or to facilitate various types of data manipula¬ tion by system controller 31, such as "stacking of data" as is well known in the art. System controller 31 also preferably communicates with a data recording medium such as tape transport 37 which is utilized to retain the data. System controller 31 will also generate timing and control signals for synchronization of system functions. Referring now to Figure 3, therein is illustrated a fiber optic connector/transceiver 18 of the type prefer- ably utilized to make all connections wherein a dual duplex fiber optic link as shown in Figure 2, is utilized. Connector/transceiver 18 has a shell or cover 42 which attaches to a mounting member 44. A rubber gasket 16 is provided to form an environmental seal between mounting member 44 and cover 42. A hollow rectangular member 48 is secured to mounting member 44 for receiving one end of a fiber-optic link 14. Members 44 and 48 may be a single integral piece. Link 14 extends through a gland 49 which is connected to one end of rectangular member 48 by a nut 54 so as to seal around link 14. The six twisted pair wires 38 in link 14 are soldered or otherwise connected to pin connectors of an electrical connector or plug 50, which is secured to mounting member 44 at the end opposite rectangular member 48. Electrical connector 50 may be of any conventional, " environmentally suitable type. Two optical fibers 34a, 34b of link 14 are terminated in fiber optic transmitter modules 54a, 64b through fiber optic connectors 66. Fiber-optic connectors 66 may be of any conventional type, such as an Amphenol SMA series connectors. Optical transmitter modules 64 may be of any conventional type such as a model no. SPX 4140 manufac¬ tured by Spectronics. The remaining optical fibers 34c and 34d are termi- nated through respective fiber optic connectors 66 in conventional optical detectors 68a and 68b. Both optical detectors 68a and 68b and optical transmitters 64a and 64b are mounted on printed circuit board assemblies (PCBs) 70, which are secured to mounting member 44. PCBs 70 contain circuitry which activates the transceivers as will be discussed more fully herein below with respect to Figures 4 and 5. PCBs 70 are connected to plug 50 such as by a plurality of wires (not illustrated). When assembled, connector/transceiver 18 provides an environmentally sealed optical cable connector which protects the transceiver and the ends of the optical fibers from being affected or damaged during field use. Connector/transceivers 18 are readily connectable to RUs 22, RTUs 16, or CCU 12 via plug 50. A lever or wrench 72 affixed to plug 50 enables connector/transceiver 18 to be locked into place when secured to a compatible, compli¬ mentary connector. Referring now to Figure 4, therein is illustrated an electrical block diagram of the photodetector receiver/ amplification circuit 80 of connector/transceiver 18. Optical fiber 34 is coupled to fiber optic detector 82 which converts the light pulses to differential electrical output pulses of opposite amplitudes. These pulses are coupled into amplifier 84 which preferably includes successive differential amplifier stages until a suffi¬ cient level is reached for logic compatibility. Amplifier 84 is provided with a hysteresis circuit 86 which provides a generally square wave pulse output from amplifier 84. Bias and symmetry restoration circuit 88 and comparator 90 are provided to assure a square wave output and to adjust the signals for proper compatibility for transistor-to- transistor logic (TTL) circuitry. Because receiver/amplification circuit 80 is AC coupled, it can power up in either logic state. A holdoff circuit 92 is provided to assure that the receiver always powers up in a single (LO) logic state. Referring now to Figure 5, therein is illustrated optical transmitter 94. An LED driver 96 and an LED 98 are provided. LED 98 is optically, coupled to optical fiber 34 such that the light which is emitted by LED 98 whenever driver 96 goes to a high logic state is trans¬ mitted over optical fiber 34. In Figure 6, photodetector receiver/amplification circuit 80 and optical transmitter 94 are shown in further schematic form. Referring now to Figure 7, therein is illustrated in three-dimensional view an RU 22 as depicted schematically in Figure 1. RU 22 includes a box 132 containing elec¬ tronic circuitry as will be described more fully later herein. RU 22 includes a detachable DC power supply or battery pack 142 for powering the electronics within box 132 and within connectors/transceivers 18 which are connected to box 132. Two connectors 144, matable with connectors 50 on connector/transceivers 18 are provided on box 132. An additional two connectors 145 are provided as alternate connections for geophone arrays (26 in Figure 1) . Rather than connecting geophone arrays 26 to takeouts 136 in links 18, geophone arrays 26 may be connected directly to remote units 22 through connectors 145 if desired. Referring now to Figure 8, therein is shown the circuitry of an RU 22, depicted in block diagram form. As shown, eight analog inputs, four from each of two standard connectors 144 or alternate connectors 145 are fed over lines 150 to multiplexer 152, which selects either stan¬ dard or alternate inputs. The analog inputs are both filtered for high frequency and amplified in quad prea ps 154 prior to being input into track- nd-hoId, instan¬ taneous floating point (IFP), and analog-to-digital (A/D) module 156. All analog input signals are sampled simul¬ taneously by the track and hold network, and are gain- ranged from 1 to 32,768 times to near A/D midscale by the IFP, as disclosed in U.S. Patent Nos. 4,104,596 and 4r,158,819, which are incorporated herein by reference. The resulting digitized mantissa and gain words for each original input or channel are fed to output formatter 158, which loads the parallel data into a serial output buffer for transmission via optical link 14 to CCU 12. Timing and control logic unit 160 functions as a controller for RU 22. It receives and decodes control data from CCU 12 through receivers 162 to initiate the sampling and digitization process. All channels are sampled simultaneously, gain-ranged, and digitized accord- ing to the control logic sequence. At the appropriate time, the timing and control logic provides digital data to transmitters 164 for transmission to CCU 12. Control pulses received from CCU 12 contain an operation code, a group of five bits which the timing and control unit decodes into remote unit setup parameters, such as OMPI standard/alternate sensor relay selection, K gain, filter selection, function generator control, etc. Power supply board 166 utilizes battery pack 142 to develop regulated voltage supplies via DC-to-DC con¬ verters. Power on/off interlock 168 is provided to enable remote unit power-up and operation when one or more cable connectors 10 are engaged, as discussed more fully below. Buzzer 167 is provided primarily for theft protection, however, it also provides indication of faulty operating conditions. Shown in Figure 9 is the logic for buzzer alarm 167. Signal CONNECTORS ON is generated when either of the two connector/transceivers is attached to remote unit 22. The signal CONNECTORS ON clocks one-shot 300 which momentarily activates the buzzer, indicating that battery pack 142 is not dead. Unauthorized disconnect register 302 and unauthorized POWER DOWN register 304 are enabled whenever the RU is powered up. The reset of these registers is controlled by CCU 12. When both connectors are removed, signal CONNECTORS OFF goes HI, AND-gate 306 is triggered, thereby energizing the buzzer. This theft protection is operable with the RU powered up or powered down. When communication to CCU 12 is interrupted, signal POWER DOWN goes HI. If unauthorized POWER DOWN register 304 is set when signal POWER DOWN goes HI, flip-flop 308 and AND-gate 310 are activated, thereby energizing the buzzer. Buzzer 67 may also be enabled by an external voltage check circuit (not illustrated) . Referring now to Figures 10A and 10B, therein is shown a block diagram of a single channel of quad preamp/filter 154. When test relay 170 is enabled to the external inputs position (as shown), geophone analog input signals are fed into preamp or K Gain stage 172. K Gain stage 172 may be remotely programmed to gains of 4, 16, 64, or 256 by register 174. Low-cut prefilter 175 receives the output from preamp 172 and serves to Low-pass filter the signal prior to it3 input into switched Low-cut filter 178. Low-cut filter 178 may be configured as an 0 (OUT), 12, 24, or 36 dB per octave high-pass filter by proper stage selection with switches 180 and 182, which are set by register 184. Low-cut corner frequency is determined by the duty cycle of low-cut frequency clocks 186, as more fully discussed below in connection with Figure 12. Low-cut filter 178 is followed by 50 or 60 Hz strap- pable notch filter 188 which is remotely selectable as either "in"- or "out" with switch 190. Notch filter 188 consists of two cascaded, stagger-tuned, second order notch filters to provide better than 60 dB attenuation over a 0.2 Hz bandwidth. Seventh order switched elliptical anti-aliasing filter 192 follows notch filter 188. The corner frequency is remotely selected by the duty cycle of alias frequency clock 194, as discussed more fully below in connection with Figure 10, at one of sixteen frequencies between 39 to 500 Hz. The preferred slope in this frequency range is 96 dB/octave MAX. It will be clearly understood that these parameters are exemplary only and that other parameters may be utilized. Anti-aliasing filter 192 is followed by post-aliasing filter 196 which removes switching transients from the signal. The output of filter 196 is AC-coupled into gain stage 198 which functions as an output buffer and gain- adjust mechanism. The output is then switched to the track-and-hoId (Figure 11) by control logic 222 using switch 200. Low-cut filter 178 and anti-aliasing filter 192 use pulse width controlled signals for controlling filter corner frequencies. Shown in Figure 11 is a schematic diagram of the switched filter control circuit 232 which generates the necessary clock pulses and provides the CCU interface for pulse width control. This circuit also synchronizes the filter switching with the control clock, thereby mini iz- ing the transient signal noise received by the track-and- hold. Clock circuit 312 divides a megahertz signal to generate a 512 KHz or 256 KHz clock signal, depending on whether anti-alias filter 192 corner frequency is set above or below 250 Hz (by CW data). The clock signal is divided by 64 in counter 314 to yield an 8 KHz or 4 KHz period for filter control. The 8 KHz/4 KHz signal is used as a reset signal for counters 316 and 318 and latches 320 and 322. Counters 316 and 318 control the pulse width of the filter control signals by setting latches 320 and 322, respectively, at a time determined by CW data. The end result is that the filter switching control period is controlled by the anti-alias corner frequency which selects either an 8 KHz or 4 KHz reset cycle. The pulse widths of the filter control signals, which correspond to the respective duty cycles, are determined by the values loaded into registers 324 and 326 (which preset counters 316 and 318, respectively) by a CW over line 328 from CCU 12. In the presently preferred embodiment, there are four preamps/filters per card, along with associated data registers and support circuitry. Two quad preamp cards 154 are provided in each box 132; however, control logic 160 can accomodate a single card. ( - - °MPΓ Figure 12 is a block diagram of track-and-hoId, IFP, and A/D module 156 of Figure 8. Each preamp (154 in out¬ put is fed into a corresponding track-and-hold (T/H) 202a202h (a total of eight) prior to reception of a CW from CCU 12. When the command is detected, T/H 202a202h are simultaneously switched from the tracking mode to the hold mode, thereby providing minimum sampling skew. According to the established box direction and sampling rate, successive channels are multiplexed by MUX switch 206 to IFP gain-ranging amplifier 208. MUX control is provided by channel address counter 210. The basic purpose of IFP amplifier 208 is to amplify the analog input signals to a value near the full-scale range of A/D convertor 212, usually between one-half and full scale, and to provide a digital code corresponding to the actual gain applied to the input signal. The signal is held constant during the gain-ranging process. This process uses a successive approximation logic sequence to apply appropriate IFP gain stages 208 to amplify the hold sample by the necessary gain 2 n , where n = o, 1, 2,..., 15. Level detector 214 is enabled at the end of each IFP gain-stage time cycle. The amplified signal is then sampled by A/D track-and-hoId 216 and converted to digital data by A/D converter 212 for trans¬ mission along with the gain code generated during the gain-ranging process. To prevent various stages of IFP amplifier 208 from introducing significant offset errors, a correction voltage is subtracted from each stage. Periodically, the offset of each IFP stage is detected by offset logic 218, and the correction voltage is incremented by a small amount in a direction that will reduce the offset. MUX averager 220 is used to correct preamp offset errors prior to gain stage amplification. • Each channel's error correction voltage is summed into its held signal to cancel the offset during its MUX time. The correction signals are updated each scan time. Control logic 222 provides the timing and control for T/H, IFP, and A/D module 156. This logic controls the T/H MUX timing, IFP gain stage switching, A/D converting, and data register storing. System size is input from RU timing and control logic (160 in Figure 8) to channel address counter 210. Four or eight channels are selected, based on the desired field spread and scan rate. When channel selection other than four or eight is required, data is still * multiplexed to IFP amplifier 208 as four or eight channels, but unneces¬ sary data is stripped before transmission to link 14 by the output formatter (158 in Figure 8). As shown in Figure 13, mask control logic 329 which is included in timing and control logic 160, controls the digitized analog data to be formatted and transmitted to CCU 12. Control is achieved by CCU 12 loading a mask bit for each channel, which enables the selection of specific channels for data input to the CCU 12. Two 8-bit regis¬ ters 330 and 332 are provided so that dynamic sampling may be achieved. As only one register is used at a time, the other register may receive updated mask bits. The transi- tion between registers 330 and 332 is controlled by CCU 12. Each analog channel is dedicated to a particular geophone group, and one of eight different MUX address codes 000, 001, 010, ..., Ill is dedicated to each channel. Whenever data is available from any one channel, _ OMPI its address code is presented to multiplexer 334. Multi¬ plexer 334 selects the corresponding mask bit for that channel and presents it to the output formatter (158 in Figures S and 14) . A "1" mask bit allows the formatter to convert channel data for transmission; a "0" causes the formatter to ignore this channel. Referring to Eigure 14, therein is shown a block diagram of remote unit timing and control logic (160 in Figure 8). Box "power on" control interlock 168 cycles power to the optical receivers (80 in Figure 5) in connector/transceivers 18 until transmission is detected, at which time the main RU power supply (166 in Figure 8) is enabled. If no optical reception occurs for a speci- fied period of time, "power on" circuitry 168 senses the inactivity and returns to the cyclic power on/off mode. Because connector/transceivers 18 are mechanically identical, box direction/box on line control circuit 224 is provided. Circuit 224 determines the direction of incidence of the first (command) signal and establishes this as the CCU direction. With this information, the RU may be set up for proper preamp multiplexing regardless of connector interchange. Referring now to Figure 15, therein is illustrated in greater detail box direction/box on line control 224 of Figure 14. Each powered-up RU begins in a repeater mode. After a CW transmitted by CCU 12 passes through a remote unit 22, signal CW RECEIVED clocks box-on-line flip-flop 336, which switches out receiver lines 338 and connects RU data formatter/encoder 158 and end-of-transmission (EOT) generator (230 in Figure 14) to the appropriate optical transmitters. The RU has now been taken out of the repeater mode and is awaiting receipt of the EOT signal from the previous upstream RU. After detecting this EOT OMPI signal (which is blocked from passing through to the next RU), RU 22 transmits its encoded data- upstream to CCU 12. Thus, the data from this RU is inserted behind the data from the previous RU. By controlling when the EOT is transmitted from the previous RU, the gap between the two data bursts is controlled. After the encoded data has been transmitted to CCU 12, the RU transmits an EOT signal to the next downstream RU. At this time, signal DATA TRANSMITTED clocks flipflop 336, which disconnects formatter/encoder 158 and EOT generator 230 and places remote unit 22 back in the repeater mode. To ensure that the entire CW has been received by the RU, the RU remains in the repeater mode for a time period of preferably nine microseconds after signal CW RECEIVED is generated. This time period is longer than the time required to receive a CW, but shorter than the time lag between the generation of signal CW RECEIVED and the EOT signal. Referring again to Figure 14, Manchester II decoder and serial-to-parallel conversion logic 226 functions as an input decoder and data formatter. Manchester II code (Man II code) is utilized because of its "sel -clocking" asynchronous format. All transmissions are burst mode Man II code to conserve power. As shown in Figures 16A and 16B, decoder and serial-to-parallel logic circuitry 226 decodes the incoming signal and stores it in a parallel register for output to CW decoder 228. As shown, a Manchester II clock pulse (Man II ck) is generated by EXCLUSIVE OR-gate 340 and inverter 342 each time a transi¬ tion occurs in the Man II code. The Man II ck clocks one-shot 344 which has a time constant of 3/4 bit cell time. The Man II ck also clocks J/K flip-flop 346, with the 3/4 bit cell time tied to the J input. The output of flip-flop 346 is Manchester II data (representative of either seismic data being transmitted upstream or command data being transmitted downstream). If a Man II ck occurs during the 3/4 bit cell time, the output of flip-flop 340 goes HI, indicating that the Man II data is a "1". The 3/4 bit cell time also clocks the Man II data into 33-bit serial-to-parallel shift register 348. If a Man II ck occurs during the 3/4 cell time, a "1" is loaded into register 348. Otherwise, a "0" is clocked into register 348. A preamble of all zeros precedes a CW. As a result of repeated transmission, the leading bits of the preamble may become distorted and decoded as a "1". To prevent false l's from being detected, preamble stripper logic 350 is utilized. When the preamble is received, the first transition of Man II code causes flip-flop 352 to go HI. This HI output is delayed by strip time RC time constant circuit 354, preferably established at two microseconds. After the time delay, one-shot 344 is allowed to fire. Flip-flop 352 is reset after all CW data is received. This CW data includes: 1. Preamble - a 24 to 56 bit all "0 ! s" data train used by optical receiver symmetry restoration circuitry 124 (Figure 4 to maintain input data integrity. RU Logic effectively ignores this segment of the CW; Sync Code - a two-bit sequence signifiying decoder start; 3. RU Address - a nine-bit code unique to each RU. RU logic ignores all codes except all "l's" and its box address. Addresses are assigned during the RU power-up sequence; 4. OP Code - a five-bit code defining the operation to be performed. For example, a box address assignment has Op Code 00000; 5. Data Word - a fifteen-bit code which is loaded into registers for preamp control box set-up (mask), function generator, etc.; 6. Stop Bit - a one-bit code, a "1" used as a data validity check bit, indicates that the data is good; 7. Delay - a calculated N bit data delay which allows each RU to dump its data onto the optical link before receiving additional data from the adjacent RU; and 8. EOT - a four-bit code which signifies end-of transmission of the CW and the start of data output to the CCU. As stated above, the CW includes a nine-bit code which is used to give each RU an individual identity in order to keep its data separate. As shown in Figure 17, nine-bit register 374 is provided in each RU, affording 512 possible different combinations. Comparator 376 is included to identify any CW box address that matches the data in register 374. All l's detector 378 is provided to detect an all l's address code. When the RU powers up, register 374 is cleared so that the box address is "000000000." -A special CW trans¬ mitted by the CCU assigns a binary number between one and 510 to the RU, as determined by the relative position of this RU with respect to CCU 12 and the other RUs 22, which is loaded into register 374. The numbers one through 510 are used as individual box addresses. An all zeros address code is used only during powering up, while an all l's code is used to enable CCU 12 to communicate with all of the RUs at the same time. Referring again to Figure 14, end-of-transmission detector generator 230 determines when an EOT code is sent to the next RU so the latter can transmit its data. As shown in Figures 18A and 18B, two individual EOT circuits control the transmission of data from the RUs. One detects the EOT transmitted from the previous upstream RU; the second generates an EOT code for transmission to the next downstream RU. The EOT detector of Figure 18A includes counter 366 which is reset and enabled when a CW is received. Counter 366 is disabled after the EOT code is received. The CW precedes the EOT code in the data stream. The time delay between them depends on the quantity of data transmitted by each RU and the position of the particular RU in the line. The more RUs between this RU and the CCU, the longer the delay between the CW and the EOT. The EOT code clocks counter 366, thereby triggering the formatter/encoder (158 in Figure 8) to begin data transmission. The EOT generator of Figure 18B is partially con¬ trolled by CCU 12. Typically, EOT transmission is com- pleted approximately one microsecond after data trans¬ mission is completed. CCU 12 can change this time differ- ential or gap by modifying the code loaded into register 358. A different code addresses another section of programmable read-only memory (PROM) 360, producing a different EOT position with respect to transmitted data (that is, changing the gap). Counter 362 counts the number of digitized analog channels which are to be trans¬ mitted. Counter 362 addresses PROM 360, and the output of PROM 360 presets counter 364. As data is transmitted, counter 362 begins counting, and the output from counter 362 allows the EOT code to be transmitted at the correct time. Preamp control logic (232 in Figure 14) determines the frequencies and duty cycles of the low-cut and anti- alias switched filter clocks 186 and 194 (Figure 10) and decodes and enables all other preamp setup and control functions defined in the preamp block diagram (Figure 10). Figure 20 is a block diagram of the output formatter/encoder (158 in Figure 8). In the presently preferred embodiment, a standard set of output data for each channel includes a four-bit gain word and a fifteen- bit data word. Output data from each RU is formatted into a sequence of words as follows: (1) a two-bit sync code; (2) a one-bit box fault code; (3) a nine-bit RU address; and (4) one to eight sets of channel data. The total word length is selected to obtain a "0" logic level at the end of transmission to conserve power between transmissions and to utilize eight-bit groups to simplify encoding. The following chart indicates the nine possible word lengths which may be transmitted from a RU 22, depending upon the number of channels being transmitted: NO. OF BITS OUTPUT DATA TRANSMITTED SYNC + FAULT + ADDRESS + 0 CHANNELS = 12 BITS 16 SYNC + FAULT + ADDRESS + 1 CHANNEL = 31 BITS 32 SYNC + FAULT + • ADDRESS + 2 CHANNELS » 50 BITS 56.- SYNC + FAULT + ADDRESS + 3 CHANNELS » 69 BITS 72 SYNC + FAULT + ADDRESS + 4 CHANNELS = 88 BITS 88 SYNC + .FAULT + ADDRESS + 5 CHANNELS = 107 BITS 112 SYNC + FAULT + ADDRESS +.6 CHANNELS = 126 BITS 128 SYNC + FAULT + ADDRESS + 7 CHANNELS - 145 BITS 152 SYNC + > FAULT + ADDRESS + 8 CHANNELS = 164 BITS 168 It is to be understood that the data output may have other formats and still remain within the scope of the present invention. As shown in Figure 20, the formatter circuit includes counter 380 to count the number of channels formatted, PROM 382 to determine how many bits need to be shifted (based on the above chart), counter 384 to count how many shifts have occurred, and first-in, first-out (FIFO) memories 386 to store the formatted data until trans¬ mission. When the CW is received, the sync bits, fault bits, and box address are loaded into shift register 388. Simultaneously, the required number of bits to be trans¬ mitted are .transferred from PROM 382 to counter 384. As shift register 388 shifts, counter 384 counts. After eight bits are shifted and presented to memory 386, a clock is generated to load the eight bits into memory. This process continues until all full eight-bit words are transferred into FIFO-memory, at which time counter 380 increments its count. Any left-over bits remaining in the shift register are used to complete the next eight-bit word. Two FIFO memories are provided so that one may be loaded with new data as the other is unloading data to the encoder circuit. OMPI Encoder circuit 387 generates the preamble, accepts and serializes eight-bit words from memories 386, and converts this serial data to Manchester II code. When an EOT code is received from the previous RU, a preamble of specified length (similar to the CW preamble) is gener¬ ated, after which an eight-bit data word from memories 386 is transferred to shift register 390. The first word transferred is the sync bits, the fault bit, and part of the box address. Register 390 shifts at an 8 MHz rate into Man II coder 392 which generates the bit cell transi¬ tions. FIFO memories 386 unload at a 1 MHz rate which matches the 8 MHz shift rate so that there is a continuous data stream out of Man II coder 392. Encoding stops when a signal from FIFO memory indicates it is empty. The final bit coded causes the output of Man II coder 392 to be at a logic LO level. Referring now to Figure 21, Man II coder 392 is enabled by taking the input to AND-gate 394 HI. During generation of the preamble, register 390 is cleared, causing all zeros data to be presented to coder 392. 0R- gate 396 causes J/K flip-flop 398 to toggle at bit cell times. Once generation o the preamble is completed, memory data is loaded into register 390. As the data shifts out, flip-flop 398 either changes state at mid-cell time when a "1" is presented to coder 392 or remains in its present state because a "0" is presented. After all data is coded, Man II coder is disabled by taking the input to AND-gate 394 LO. Referring now to Figure 22, therein is shown a block diagram of the function generator (169 in Figure 8). Test signals are generated sample by sample in digital form by CCU 12. This digital signal is then transmitted to the RUs as a part of the CW. In the RUs, the digital signal is converted to an analog signal with a near full-scale OMPI peak value by digital-to-analog (D/A) converter 240. The resulting analog signal is attenuated- to the desired amplitude by digitally controlled attenuators 242 and 244. The LO level analog signal is then fed into preamp oscil- lator.inputs 201 for test purposes. Figure 23 is a block diagram of the battery pack and power supply 142 and 166, respectively, in Figure 8. Battery pack 142 includes two 12 volt lead-acid batteries connected in series with a common output. When a con¬ nector/transceiver 18 is engaged with a remote unit connector 144, interlock circuitry (168 in Figure 8) is enabled. Optical receivers 92 are cycled on and off to conserve power until light transmission is detected. Signal VREG ENB then goes HI to force power on/off control 246 to enable soft-start circuitry 248 and main power relay 250. Power is distributed to two DC-to-DC con¬ verters 252 and 254. Resulting outputs are filtered with high-cut filters 256, 258, and 260 prior to distribution for various box functions. Secondary relay 262 must be thrown to enable power to the function generator (169 in Figure 8) . Referring now to Figures 24 A and B of the drawings, therein is shown in three-dimensional view a RTU 16 in accordance with the present invention. RTU 16, like RU 22 includes a box 700 suitable for protecting the electronics contained therein from the environment. Box 700 includes four connectors 702, each of which is matable with plug 50 on connector/transceiver 18. Two of connectors 702 are designated as command parts Cl and C2 and are utilized for coupling to the CCU or to other RTUs. The remaining two connectors are each ports to the HI and LO sides of the line in which the RTU is placed. OMPI Referring now to Figure 25, therein is shown the electronics within RTU 16, depicted in block diagram form. Connector/transceivers 18 are depicted to indicate signal inputs/outputs to CCU 12 and to a serially connected RTU (at Cl and C2) and between RTU 16 and adjacent RTUs 22 (labeled "HI" and "LO"). Two CW carrying optical fibers 710a, 710b, and two return data optical fibers 712a and 712b are coupled through connector/transceivers 18 at Cl and C2, and circuitry connected thereto, to CW/data multi- plexer and master control circuit 714. Multiplexer and master control circuit 714 includes circuitry whic controls both the common functions of RTU 16, i.e., those functions related to the RTUs power regulation and data handling functions, as well as portions of both LO-side and Hi-side system control functions such as signal steering controls. Multiplexer and master control circuit 714 is then coupled to LO-side control electronic 716 and Hi-side control electronics 718, each of which 716 or 718 is dedicated solely to signal handling for its designated side of the line in which RTU 16 is placed. RTU 16 includes a power supply 720 which is controlled by power on-off control 722. Multiplexer and master control 714 is also coupled to common CW decoder 724 and common RTU data encoder 726 which facilitates the response of the RTU to command signals from the CCU. Referring now to Figure 26, therein is illustrated power supply 720 of RTU electronics 700 in greater detail. A battery pack (not illustrated) such as that previously described with respect to RU 16 is coupled through relays 730 for each of the common, HI, and LO circuitry to DC- to-DC converters 734 to provide plus and minus 5 volts to each of Hi-side logic and LO-side logic and provide plus and minus 12 volts and plus 5 volts to common logic. ■ JΪ A OMPI Referring again to Figure 25 a soft start circuit 731 is provided, as in the RUs, to supply power to the con¬ tacts of relays 730 to prevent current surges upon relay operation which might damage the relays. Voltage fault detect circuitry 733 generates a fault bit if the battery pack (not illlustrated) becomes discharged. This fault bit is then communicated to RTU data encoder 726 for transmission to the CCU in the RTU status signal. Control of power supply 720 comes from power on-off control circuit 722. When a connector/transceiver 18 is connected to control port Cl or C2, the battery (not illustrated) is jumpered to create an INTERLOCK signal. This INTERLOCK enables power on-off control circuit 722 to power con¬ nector/transceivers 18 at controls Cl and C2 on a cyclical basis; for example, in one preferred embodiment, 18 milli¬ seconds on, 250 milliseconds off, until a valid CW signal is received. Upon receipt of an appropriate CW, power on-off control circuit 722 then supplies power on signals to power supply 720 enabling power to the COMMON and designated HI and/or L0 sides. During operation of the RTU, power on/off control circuit 722 monitors the LO and Hi-side CW and, upon cessation of a CW to either side, an automatic POWER DOWN signal is enabled to that side. Referring now to Figure 27, therein is illustrated common circuitry of multiplexer and master control circuit 714 in further block diagram form as well as common CW decoder 724 and common RTU data encoder 726. Fiber optic CW lines 710a and 710b from Cl and fiber optic CW lines coupled to C2 are coupled directly to both box direction control circuitry 740 and CW data multiplexer circuitry 742. Box direction control circuitry 740 is utilized to orient the RTU within the ground system; i.e., to determine which command port will be designated as Cl, linked to the CCU. The CW selector 744 receives CW input signals from the CCU. The signal then passes to CW decoder 724 where the CW is interpreted and transmitted to opcode logic 728. Bo ' x direction control circuitry 740 is shown in- more detail in Figure 28. Box direction control 740 recognizes the connector/transceiver 18 from which the first CW is received and designates that connector as Cl, i.e., the connector/transceiver 18. of the link coupled directly to the CCU. A logic level indicating the connector to be designated as the control port is then communicated to CW/data. multiplexer circuit 742 illustrated in Figure 29. CW/data multiplexer 742 then appropriately routes signals. Between each command port fiber optic receiver line and the appropriate data restoration circuit (715 or 717 in Figure 25) and between LO-side steering logic for RU, LO, RD and RTU LO CWS and transmitter to the appropriate com¬ mand port fiber optic transmitter. As indicated in Figure 29, Hi-side signals are switched in the same manner by CW/data multiplexer 742 in response to the CCU direction signal from direction control circuit 740. Referring back to Figure 27, CW selector 744 is utilized to determine whether RTU data will be transmitted to the CCU on the HI or LO side. Because it is only necessary.to transmit the RTU data once, one side, such as the LO side, is preselected to carry the RTU data, if that side is powered by power on/off control circuit 722. If the preselected side is not powered, such as, if there is not a POWER LATCH ENABLE LO signal to CW selector 744, then selector 744 will allow the RTU data to be trans¬ mitted to CCU on the HI side. CWs addressing the RTU need similarly be communicated across only one line. After selecting the side from which the CW (and EOT) will be accepted, these signals are then communicated to CW decoder 724. Referring now to Figure 31, therein is shown CW decoder 724 in further block diagram form. The selected CW and EOT signal pass to preamble and EOT stripper 750 which removes the preamble and EOT groups contained in the CW to prevent erroneous decoding errors. At this point, a CW and a format as follows may be utilized for addressing a RTU. RU RU RTU RTU RTU Stop Sync Adrs OpCode Adrs OpCode Data Bit 10 000 0B XXXXX 00000 DDDDD 1 RU OpCode OB is a NO-Op to the RUs. A 5-bit RTU address field provides for up to 32 possible combinations. In a presently preferred embodiment, an RTU address of all zeros is utilized for an RTU power up sequence and an RTU address of 31 is utilized for commands to all RTUs. This therefore facilitates the addressing of 30 individual RTUs. The OpCode and the RTU data field facilitate the control of the RU. As will be seen from the following chart, an OpCode of 00 enables the assigning of a new address to the RTU such address indicated by the 5-bits in the data field. An OpCode of 01 enables the last 2-bits of the data field to be utilized to turn the C2 command port transmitter on each of the HI and LO sides. An OpCode of 03 enables 4-bits of the data field to control both command port C2 receivers and HI and LO port receivers on an OpCode of 05 facilitates the operation of the RTU Cl transmitter. OMPΪ Opcode Data A B c D ε 00 A A A A A 01 X X X H L 03 X H H L L 05 X X X X T The CW, minus the preamble and EOT then passes to Manchester II decoder 752 which changes the CW from the Manchester II self-clocking format to a more conventional type of serial data format using a parallel clock. The decoded data in serial form is then converted into parallel form in serial-to-parallel converters 754. If the CW contains an RTU address qualifying signal, the CW RTU address is then compared to the RTUs assigned address by box qualifier 756 to determine if the RTU will respond to the CW. Referring to Figures 32 and 33, preamble and EOT stripper 750 is depicted in Figure 32 and Manll decoder is depicted in Figure 33. The first transition of Man II code causes flip-flop 758 to go HI which is delayed from transmission by RC time constant circuit 760. After the established time delay, preferably on the order of 2 microseconds, the preamble stripper signal on line 759 allows one shot 762 to fire. After all CW data is received, flip-flop 758 is reset by RC time constant circuit 764 and the Manchester II data is clocked into shift register 766. The RTU OPCODE and data field are communicated to opcode logic circuit 728. Opcode logic circuit 728 preferably loads registers with data from the RTU data buss. Opcode logic 728 communicates the instructions contained within the OPCODE to output port enables which selectively control transmitter and receiver operation at the control ports in the manner described earlier herein. CW decoder 724 also will preferably include timing and control circuitry responsive to the CW for generating timing signals which may be utilized to control the pre¬ amble and EOT stripper 750 and box address and qualifier 756, in addition to HI and LO-side EOT detectors (in EOL detector 786 in Figure 35). An additional EOT detector is included within CW decoder 724 to generate an EOT signal in the RTU when the EOT is received from the CCU. The EOT signal from the CCU is then passed to the adjacent RU on the RTU data side. When all RU data on the designated return data side has been transmitted, the RTU EOT signal is sent to RTU data encoder 726 to start the RTU returning either its data, or its status signal. Referring now to Figure 34, therein is shown RTU data encoder, (726 in Figures 26 and 27) in block diagram form. RTU data encoder 726 serves as a data collector for information to be transmitted to the CCU. RTU data encoder 726 accepts parallel data inputs of the RTU address, and the fault bit from the RTU power supply (720 in Figure 25): RTU RTU Sync Fault RTU Ident Adrs Non-Designated 1 0 F 111111111 XXXXX 15 Zeros These data inputs are entered into parallel-to-serial converters 770, such as may be formed utilizing a plu¬ rality of shift registers, from which the data is trans¬ mitted to a Man II encoder 772. The RTU data from parallel-to-serial converter 770 and a preamble signal from preamble generator 774 enter OR gate 771. During generation of a preamble by preamble generator 774, shift registers in parallel-to-serial converter 770 may be cleared causing all zeros data to be presented to Manchester II coder 778. OR gate 776 along with ENCODER POWER SIGNAL causes EXCLUSIVE OR gate 780 to generate a Manchester II clock pulse each time a transition occurs in the Man II code. As the data shifts from parallel-to- serial converter 770, J/K flip-flop 782 toggles, coding all the RTU data which is then transferred to LO/HI STEERING LOGIC. To reduce power consumption, RTU data encoder 726 is preferably powered off between RTU data cycles by controlling the V supply to the circuit. As will be discussed more fully later herein, an end-of-line (EOL) signal will be generated. This EOL signal denotes completion of RU return data on the RTU return data side. EOL selector 727 monitors incoming data from both the HI side and the LO side. As data comes in from each RU, the data signal will return followed by a gap during which an EOT signal is sent from the trans¬ mitting RU to the next RU instructing that next RU to transmit its data. When this gap exceeds a predetermined limit, EOL selector 727 will generate the EOL signal to instruct RTU data encoder 726 to transmit the RTU data or status signal to the CCU. Also included within multiplexer and master con- troller (714 in Figure 25) is line steering and EOT . regeneration circuitry 780, depicted in Figure 35. Cir¬ cuitry 780 is present for both the HI and the LO sides, therefore only the LO side circuitry will be described here. The restored return data from all of the RUs is grouped together with the RTU return data by multiplexer 782. Another multiplexer 784 groups unrestored, or actual received data from both RU LO and RTU LO receiver inputs to- form a LO-side return data signal which then passes to symmetry restoration circuitry 717. Multiplexer 784 switches between RU LO data and RTU LO data in response to the EOL signal generated as discussed above. When cir¬ cuitry 786 detects an EOL, multiplexer 784 switches to transmit RTU LO data. After completion of this RTU data transmission, an EOT signal is delayed during the trans¬ mission of RTU data and is then passed on to the next RTU to enable the transmission of data from the next line. Line steering and EOT regeneration circuitry 780 is further depicted in schematic form in Figure 36. Referring again to Figure 25, therein i-s shown HI- side circuitry 718, including CW symmetry restoration circuitry 719 and return data symmetry restoration circuitry 721, and LO-side circuitry 716, including CW symmetry restoration circuitry 715 and return data symmetry restoration circuitry 717. HI and LO-side symmetry restoration circuitry 719 and 715, respectively, are essentially identical and HI and LO-side return data symmetry restoration circuitry 721 and 717, respectively, are essentially identical; " therefore, only LO-side restoration circuits 715 and 717 will be detailed here. Referring now to Figure 36, therein is shown CW restoration circuitry 715 in block diagram form. The CW data multiplexer (742 in Figure 27 and Figure 29) inputs LO side CW signals from CW data multiplexer 742 which utilizes an 81.92 MHz clock in conjunction with a divide- by-20 ring counter to yield a 4.098 MHz synchronized clock for CW reclocking. Flip-flops in ring counter 790 are reset at the first detected CW edge. A binary counter 794 causes the CW data to set flip-flop 792 which instructs multiplexer 796 to switch the EOT LO signal to the appro¬ priate output. Referring now to Figure 37, therein is shown LO-side RU return data restoration circuitry 717. LO-side return data is input to restoration circuit 717 from CW data multiplexer (742 in Figure 27). Retriggerable one-shot 798 forms an envelope around the CW signal. The CW passes to restoration flip-flop.799 which is clocked by a 16.384 MHz clocking signal from divide-by-5 Johnson counter 800. The restored LO-side data is then input into multiplexer 782 of line steering and EOT regeneration circuitry (780 in Figure 35). In a seismic survey system as described herein, each RU 22 has a specific address by which CCU 12 will communi¬ cate a CW to that RU 22. Similarly, CCU 12 may selec- tively instruct each RU 22 to mask out any one or more data signals from the geophone arrays 28 coupled to that RU 22. The same address which is utilized to identify each geophone array 26 is also used to keep track of the placement of each seismic "shot" or energy source from w- hich energy will be recorded by geophone arrays 26. This capability to identify shot placement and individually access data from specific geophone arrays 26 facilitates optimal flexibility and efficiency in three-dimensional seismic surveying. Referring now to Figure 39 therein is illustrated one shooting pattern which is practical with a system as disclosed herein. A grid is established composed of, in this case, five lines 600, 602, 604, 606, and 608. Each line includes 12 flags or stations, numbered 611-622. Each "X" represents a geophone array on the lines. A shotpoint may be indicated to the system through reference to an adjacent line and station number. For example, in a pattern as indicated, first shot location 623 may be indicated by a three digit code indicating the line which the shot is on or the lowest adjacent line number. In OMPI this case, the shot is on line 500 which may be established solely for purposes of reference of the shotpoint. Therefore, utilizing a three digit line identification code, this shotpoint may be indicated on the X-axis located at line 600. Because the shot is on the line, and not between lines, the next identifier of the identification code, a between line reference, may be 0. Finally, the Y-axis of the shot location may be indicated through reference to the next lowest station number, utilizing a four digit station, code 0615. Each shot on the system grid may be identified in this manner. Where a shot occurs between lines, the fourth digit of the eight digit number, the between line reference, may be utilized to indicate which shot between line shotpoint t location the shotpoint represents. For example, shotpoint location 624 is the only between-line shot between lines 604 and 606 and is therefore "1" of "1" shotpoints between those lines. Shotpoint 624 may thus be identified by an eight digit code: 602-1-0615. In this manner, it is possible to keep track of all shotpoints and record their location relative to the multi-line configuration. Further, it is now possible to accomplish both station roll and line roll operations. This facilitates optimal flexibility in the sequence of shot placement. For purposes of example only, if it were desired to accumulate data for a six station split spread relative to the shotpoint; i.e., a spread of three sta¬ tions on the grid to each side of shotpoint, rolling the shotpoint for shotpoints 623-629 geophone stations 613- 618 on lines 600, 602, 604, and 606 would be utilized for accumulation of data. As the shotpoint location is advanced to the location of shotpoint 630, a station roll may be accomplished by CCU 12 whereby data will be accumu- lated from stations 614-619 on lines 602, 604, 606, and 608. This sequence can then be continued as desired. OMPI When this shooting pattern across lines 602-608 has been completed as desired, lines 602-608 may be powered down by appropriate CWs from the CCU and the lines rolled; i.e., an additional set of lines (not illustrated) powered up such that the sequence may begin again. Because the shotpoint location is identified to the CCU, the shotpoint may roll along starting from left to right along one set of lines and may then roll along stations from right to left on the next set of lines while still maintaining a record which is readily interpretable by data processing equipment utilized to process the acquired data into a three-dimensional record. Additionally, within limits of the channel handling capacity of the CCU and the particular convention utilized for station addresses, because of the individually addressable RUs and RTUs it is possible to roll from one line to another in response to the movement of the shotpoint. Referring now to Figure 40, therein is illustrated a "Z" shooting pattern which may optionally be employed by this system in a manner similar to that described to accomplish a "loop" shooting pattern. Because seismic energy expands radially from a shot- point and dissipates as it travels away from the shot- point, it is often desirable to vary or "taper" parameters of geophone arrays such as the preamplifier gain (K gain) on the geophone arrays in response to their distance from the shotpoint. The present invention facilitates the establishing of these parameters relative to a shotpoint for each individual line within a multi-line system. Again for example only, around shotpoint 637 in Figure 41 are a variety of geophone arrays, as described with respect to Figure 39. The RUs (not illustrated) may be instructed by to establish a first K-gain on geophone arrays located within circle 633, i.e., stations 616 and 617 on lines 604 OMPI and 606. Similarly, a second K-gain may be established at those stations within circle 634, i.e.,. stations 615- 618 on lines 602 and 608, and stations 614, 615, 618, and 619 on lines 604 and 606. Alternatively, selected geo- phone arrays such as those located within circle 633 may, instead of being fixed with a first incremental gain, have their received data masked within the RUs (as discussed with regard to Figure 13) such that no data will be recorded from those arrays. Again within the capacity of the system as described earlier herein with regard to Figure 39, upon instruction from the CCU, the ground electronics of the system may advance these taper para¬ meters with the shotpoint. Referring now to Figure 42, therein is shown a seismic survey system including both "standard" geophone arrays and alternate geophone arrays. In conventional single-line seismic survey systems, it is known to utilize alternate geophone arrays distributed in various array patterns to attenuate/horizontally propogated energy which may be encountered in survey operations. For example, a linear geophone array weighted in a Chebychev function can reduce horizontally propogated energy by forty dB over a wide range of frequencies. This is discussed more fully in U.S.- Patents 4,024,492 and 4,151,504, the specifications of which are incorporated herein by reference. Areal arrays, though giving more uniformed characteristics from different azimuth arrivals, cannot duplicate the attenuation achievable with a Chebychev weighted function, even if the arrays include many times the number of geophone elements. For a linear array, the effective length of the array is reduced as the cosine of the arrival angle. Thus, at 45 degrees the apparent length of the line?r array is OMPI , WIPO reduced to approximately 70.7 percent of the actual length of the array and the frequency of the attenuated region is increased as a result. The attenuation is still 40 db in the reject band, and thus promotes greater efficiency in reducing horizontally propagated energy than does an areal array. With a standard/alternate geophone array system, having the linear arrays disposed at 90 degrees to one another, as the arrival angle passes beyond 45 degrees, the input may be transferred from one array to the other, thereby causing the apparent array length to increase again as the arrival angle approaches 90 degrees.. Therefore, with multi-line seismic survey systems, because the shotpoint will typically move perpendicularly to some lines, it is preferable to selectively utilize either standard or alternate geophone arrays at each station so as to minimize these phenomenon in each portion of acquired data. Therefore, data may be selectively addressed from either standard or alternate geophone arrays at each station. For example, in the example of Figure 42, optimal data acquisition could be obtained by utilizing alternate geophone arrays 635 in quadrants A and C around shotpoint 637 and utilizing standard geophone arrays 26 in quadrants B and C around shotpoint 637. When gaps, tapers, or alternate arrays are rolled with the shotpoint, the system must be programmed as to how to advance the gaps or tapers when the shotpoint advances to a position between lines or stations. Referring now to Figure 43, therein is shown a flow chart depicting initial setup of a seismic survey system in accordance with the present invention. The CCU is first powered up 900. At this time the system operator will input parameters relating to the survey operation which he wishes ' to conduct 902. These parameters will then be read by the system. Once this is done, the system will determine if a multi-line operation has been selected 904. If "yes", the system will set flags for multiline 906. The system will then accept operator input data as to line numbers and location and as to shot line numbers and between line shot numbers. If "no", the system will set flags for non-multi-line, i.e., single line operation 907. If multiline operation has been selected, the system will determine if tapered lines have also been selected 908. If yes, then the system will set flags to accept data regarding the tapered lines parameters 910. If "no", the system will not accept tapered line data. The determination will then be made if the operator has decided to perform scatter shooting 912, i.e., randomly placed shot points rather than an established pattern. If "yes", the system is set to accept individual shotpoint indexes 914. If "no", a decision is made as to whether a loop shot advance (as depicted in Figure 39) has been selected 916. If "yes", the system sets flags to accept data regarding the parameters of the loop advance. If "no", the system sets flags to accept data for a "Z" advance as depicted in Figure 40. As discussed previously herein, once the system is set up and the operator elects to power up the lines, as optical link including connector/transceivers 18 is connected to each RU or RTU, a portion of the internal electronics of the RU or RTU powers up periodically looking for communication in the form of a CW from the CCU. When the RU or RTU sees the CW it fully powers up with an address of all zeros. The unit is then operational until communication between the CCU and that unit stops. When this happens, the unit will then power down after an elapsed period and go into momentary power cycling. During power up, when the CCU needs to power the ground units, it must power the RTU units first. The CCU will send a CW to the first RTU at which point that RTU will stop cycling. When the CCU receives a status signal from the RTU, it will then assign an address to the RTU and instruct the RTU to turn on its transmitter so that the CW may be communicated to the next connected RTU. After all RTUs are powered up, the CCU will preferably power up each RU on the first line and will then move to the next line and power up all RUs on that line until the entire system is powered up. Referring now to Figures 44 A-B, therein is depicted a flow chart indicating a system set up procedure for multi-line operation including a tapered line operation. As depicted in Figure 1, the line at which the CCU is located may be entered. In Figure 1 this would be at line 20a which is the electrical placement of the CCU. Next, the flag designating the electrical placement of CCU is entered 932. In a system such as that depicted in Figure 1, wherein each RU accommodates a group 27 of geophone arrays 26, this electrical placement will typi¬ cally be physically offset to one side of RTUs 16 by four stations. The number of channels per line is entered 934. Typically, one channel is assigned to each geophone array 26. The number of lines in the system is then input 936. Where a pattern of shooting has been selected, the opera¬ tor must instruct if there is a shot on line 938. If "yes", then a flag is set for later acceptance of data 940. If "no", then step 940 is bypassed and the number of shots between lines is entered 942. The operator then establishes where he wants the next shot to occur 944. This may or may not be the beginning of the pattern. If the next shot is to occur between lines, he should indi¬ cate which of the between line shots is to fire, i.e., if there are two shots between lines the operator must indicate which of these two shots is to occur next. By entering the between line reference number 946 the oper¬ ator then inputs the flag of the adjacent lower station number 948 to indicate the Y coordinate for the shotpoint. The operator then enters the shotpoint starting and ending roll parameters 950-956. The operator is establishing delimiters on the shotpoint rolls in the chosen pattern. The start line of the shotpoint is established 950, and, if the initial shotpoint of the pattern is between lines then the between line reference number is input 952. If the shotpoint is to end on-line then that coordinate is given 954, if the shotpoint is to end off of a line then the between line reference number is input 956. Parameters are then set up regarding the geophones to be utilized at each time. A decision is made as to whether a symmetrically split spread is desired 958. This would indicate that an equal number of geophone arrays (26 in Figure 1) to either side of the shotpoint will be used to collect data. If a symmetrically split spread is desired then a flag is set accordingly 960. If not, selection array configuration is deferred to a later time. The line number on which Channel 1 will be located is then input 962. A selection is made as to whether Channel No. 1 will be toward the high flags or toward the low flags 964 and the system is established accordingly 966. A selection is made as to whether Channel 1 direction is at low lines 968 and the system is then set accordingly 970. At this time the system may be set up for tapered lines operation including gap spacing. If a gap is to be utilized around the shotpoint, then the stations around the shotpoint from which data is not desired are entered 972. These stations are entered in response to the next OMPI shotpoint location which was established in steps 938-948. The system checks to see if the split spread was previously selected 974. If "yes", then the system goes on to roll direction parameters. If "no", then a channel which is desired is entered 976 and a station flag corresponding to that channel is entered 978 to allow the system to orient the gap. The program then goes on to determine roll direction parameters. If the roll direction at the end of the first shot sequence is to high flags 980, then the step size is input 982. If the roll direction is to low flags, then that alternative is entered 984 prior to input of step size 982. The system is instructed as to when to turn on as yet unused RUs as they are approached by the roll. This facilitates advance checking of the system. If any takeouts, (corresponding to stations, and RU preamp channels), are skipped, then such data is also entered 988. The number of channels per RU is input and the station flags establishing the upper and lower limits of the roll procedure are input 998 and 1000. A check is made of the initially powered RUs to see if they are operative 1002. Appropriate signals are then indicated as to the status of the RUs 1004,1006. Next, tapered line parameters are entered 1007-1012. If alternate array channels are to be selectively utilized as depicted in Figure 41, then the channels for which alternate arrays are selected are input for each line 1008. Similarly, if incremental K-gain levels are desired on selected geophone arrays as depicted in Figure 40, then those channels are indicated 1010. This is repeated until those parameters have been entered for the desired number of lines 1012. Referring now to Figure 45, therein is shown a flow¬ chart indicating how one embodiment of the seismic exploration system may move the shot point record and the data recording channels in accordance with the pre- determined desired shooting pattern as established above. As will be appreciated from the Figure, the system refers to the shotpoint location and shotpoint roll parameters previously entered into the system and keeps track of the movement of the shotpoint and correlates the appropriate channels for recording data. The shotpoint is recorded by CCU 12 in response to data obtained at each shot point, preserving an optimal data record for later processing. In advancing the shot point and the recording channels, CCU 12 first determines the direction in which the shot point is to roll. An inquiry is made as to whether the shot start line is greater than the shot end- line 1020. If "yes", the shotpoint will be advanced in a first direction 1024, toward lower numbered lines. If "no", a flag will be set to advance the shot point in a second, opposite, direction 1022. An inquiry is then made as to whether the shot start line is equal to the shot end line 1026. If "no", then the shot step is equal to the shot step plus the direction of roll 1034, If "yes", then another inquiry is made as to whether the shot start step is less than the shot end step 1028. If "yes", then a flag is set to roll the shot point in a first direction 1032. If "no", then a flag is set to roll the shot point in a second, opposite, direction 1030. The shot step is either incremented or decremented in response to the established direction 1034. An inquiry is then made if the shot start step is greater than the shot between lines 1036. If "no", then the routine ends 1038. If "yes", the shot line is either incremented or decremented in response to the established direction 1040. An inquiry is then made as to whether the shot line has exceeded the boundries as defined by the established end line direction 1042. If "yes", then the roll is affirmed 1046. If "no", an inquiry is made as to whether the shot is on line 1044. If "yes", the shot step is set equal to zero and the shot should be placed on the next line. If "no" a shot step is flagged 1050 and the next shot should be placed between lines. An inquiry is then made if the roll is to continue 1052. If "no", the routine ends 1054. If "yes", an inquiry is made as to the advance type 1056. If a first advance type is set, indicating a loop advance, CCU 12 reverses the order of the start and end lines and reverses the order of the start and end steps 1058. If a second advance type set, for a Z-advance, then the shot line is set equal to the start line and the shot step is set equal to the start step 1060. At this point, the system has accounted for rolling the shotpoint. The system will then handle rolling of channel selection in reference to the shot point. An inquiry is made as to whether the shot points will be scattered 1062, as described earlier herein. If "yes", then a flag is set to instruct the operator to input the new shot point 1064. If "no", then the shot flag is set equal to the shot flag plus the step size 1066. After this is determined, an inquiry is made as to whether there will be tapered lines 1068. If "yes", then an inquiry is made as to whether new gaps are desired 1070. If "yes", then the operator is prompted to input the new shooting gaps 1072. If "no", then an inquiry is made as to whether new channel sets are desired 1074. These new channel sets would include parameters as discussed earlier herein such as gaps, varied K-gains, or standard or alternate arrays. If new channel sets are selected, the operator is prompted to input the new channel sets 1076. Steps 1070-1076 are bypassed if tapered lines are not selected in the initial inquiry 1068. An inquiry is then made to whether a special shot point is desrired 1078. If "yes", the operator is prompted to input a special shot point number 1080. If "no", then the data recording channels are appropriately advanced 1082. The CCU then generates and transmits the appropriate addresses and command words to the RUs to appropriately program the RUs with the selected K-gain and masking data to establish gaps; program auxiliary channels; and program standard or alternate geophone arrays. The system is then ready to start the recording 1086 in coordination with the shot. Many modifications and variations may be made in the techniques and structures described herein without depart¬ ing from the scope of the present invention. Accordingly, the embodiments described and illustrated herein are illustrative only and are not intended as limitations on the scope of the present invention.

Claims: The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 1. A seismic survey system, comprising: a plurality of data lines; a plurality of geophone arrays coupled to each of said data lines; and means for selectively obtaining data from one or more of said geophone arrays. 2. The seismic survey system of Claim 1, wherein groups of said geophone arrays are coupled to control units and wherein said means for selectively obtaining data from one or more of said geophone arrays comprises a central control unit, said central control unit adapted to address said control units and further adapted to receive data from said control units. 3. The seismic survey system of Claim 2, wherein said control " units are adapted to selectively transmit data to said central control unit. 4. The seismic survey system of Claim 2, wherein said control units are adapted to selectively transmit data to said central control unit in response to a signal from said central control unit. 5. The seismic survey system of Claim 2, wherein said control units are physically removed from said central control unit. 6. Apparatus for conducting multi-line seismic survey¬ ing, comprising: a plurality of seismic sensor arrays, said sensor arrays arranged in a plurality of survey lines; and means for selectively controlling parameters of said sensor arrays. 7. The apparatus of Claim 6, wherein said means for selectively controlling parameters of said sensor arrays comprises: a central control unit adapted to generate command instructions regarding said parameters of said sensor arrays; and means for communicating said command instructions to said sensor arrays. 8. The apparatus of Claim 7, wherein said means for communicating said instructions to at least some of said sensor arrays comprises auxiliary control units coupled to groups of said sensor arrays, said auxiliary control units for receiving and controlling data from said sensor arrays. 9. The apparatus of Claim 7, further comprising fiber optic links for communicating data between said central control unit and said auxiliary control units. 10. The apparatus of Claim 8, wherein one of said con¬ trolled parameters of said sensor arrays is the signal amplitude from said sensor arrays. 11. A seismic survey system, comprising: a central control unit; a plurality of data lines; and means for facilitating signal communication between said central " control unit and said data lines, said communication means at least partially comprising a fiberoptic link. 12. The apparatus of Claim 11, wherein said system includes a fewer number of fiberoptic links between said data lines and said central control unit than the number of lines in said plurality of lines. 13. A seismic survey system, comprising: a central control unit; a plurality of data lines, each data line having a plurality of geophone arrays coupled thereto; means for recognizing- an .addressing..eac .of..said plurality of geophone arrays; and means for monitoring the location of the seismic energy source in response to said means for recognizing and addressing said geophone arrays. 14. A method of seismic surveying, comprising the steps of: establishing a plurality of data lines, each data line including a plurality of geophone arrays coupled thereto; and selectively obtaining data from at least a portion of said plurality of geophone arrays. 15. A method of seismic surveying, comprising: establishing a plurality of lines; establishing a plurality of geophone arrays on each of said plurality of lines; establishing a coordinate reference for each of said geophone arrays; and utilizing said established coordinate reference to monitor the location of a seismic shotpoint; and accessing data from at least a portion of said plurality of geophone arrays in response to said monitored shotpoint location.. 16. A seismic surveying system, comprising: a plurality of lines, each line comprising, a plurality of geophone arrays for obtaining seismic data, a plurality of control units, each of said geophone arrays coupled to one of said- control units, said control units adapted to receive data therefrom, said control units in each line communicatively coupled to one another; a central control unit communicatively coupled to said control units, said central control unit adapted to selectively address each of said control units and to receive data therefrom. 17. The seismic surveying system of Claim 16, wherein said central control unit selectively addresses each of said control units by a command word addressed to that control unit. 18. The seismic surveying system of Claim 16, wherein said control units in each line are communicatively coupled to one another in series. 19. The seismic surveying system of Claim 18, wherein said control units are communicatively coupled together by fiber optic links. 20. The seismic surveying system of Claim 18, wherein each of said lines is communicatively coupled to an adjacent line and to said central control unit. 21. The seismic surveying system of Claim 11, wherein each of said data lines comprises: a plurality of geophone arrays; a plurality of remote data acquisition units, each of said geophone arrays coupled to one of said remote data acquisition units, said remote data acquisition units communicatively coupled to one another; a recorder takeout unit communicatively coupled to said remote data acquisition units and to said central control unit and to recorder takeout units in other lines. 22. The seismic surveying system of Claim 21, wherein said recorder takeout unit contains signal steering circuitry to facilitate communication between said central control unit and any one of said remote data acquisition units. 23. The seismic surveying system of Claim 21, wherein each of said remote data acquisition units in each line and the recorder takeout unit in such line are coupled together by fiber optic links and wherein said recorder takeout unit in each line is coupled to another recorder takeout unit in an adjacent line through a fiber optic link. "g JR OMPI 24. The seismic surveying system of Claim 23, wherein each of said fiber optic links comprises: a fiber optic cable; and a pair of cable connectors, one connector coopera¬ tively coupled to each end of said fiber optic cable, each connector comprising, a fiber optic transmitter cooperatively arranged - with a first of said optical links in said fiber optic cable, driver circuitry cooperatively associated with said fiber optic transmitter, an optical detector cooperatively arranged with a second of said-optical links in said fiber optic cable, and amplifying circuitry cooperatively associated with said optical detector. 25. The seismic surveying system of Claim 24, wherein each of said fiber optic cables further comprises: a strength member extending longitudinally through the cable; and a plurality of wire conductors. OMPI 26. The seismic surveying system of Claim 21, wherein each of said remote data acquisition units includes data ■restoration circuitry for reducing data distortion in the system. 27. A seismic exploration system, comprising: a plurality of remote seismic data acquisition units; a plurality of geophone arrays, cooperatively arranged with said remote seismic data acquisi¬ tion units to form a plurality of seismic lines, each geophone array coupled to one of said remote data acquisition units; a central control unit; a plurality of fiber optic links for interconnecting adjacent remote seismic data gathering units in each seismic line in series and for intercon¬ necting said serially connected remote data acquisition unit ' s and said central control unit, each of said fiber optic links comprising, a fiber optic cable including at least two optical fibers and a plurality of wire conductors, and a pair of cable connectors, one connector coupled to each end of said fiber optic cable, each connector having a digital, logic compatable optical transceiver, said optical transceiver including a fiber optic transmitter, driver circuitry associated with said fiber optic transmitter, an optical detector, and amplifying circuitry associated with the optical detector; means associated with said central control unit for generating a distinct command word for selec¬ tively addressing one of said remote data acquisition units; means associated with said central control unit for generating a command instructing one of said remote data acquisition units to transmit obtained data to said central control unit; and means associated with each remote data acquisition unit for generating a third command signal for instructing an adjacent remote data acquisition unit to transmit obtained data to said central control unit. 28. The seismic exploration system of Claim 27, wherein each remote data acquisition unit includes circuitry to preamplify, filter, gain range, and digitize analog seismic data from said geophone arrays coupled to said remote data acquisition unit. 29. The seismic exploration system of Claim 27, wherein each remote data acquisition unit includes mask control circuitry responsive to said first command signal for selectively transmitting data from said plurality of data channels to said central control unit. 30. The seismic exploration system of Claim 27, further comprising a plurality of recorder takeout units, one recorder takeout unit in each of said seismic lines, for facilitating communication between each of said seismic lines and said central control unit. 31. The method of seismic surveying of Claim 14,-wherein each of said data lines further includes: a plurality of remote data acquisition units, each of said geophone arrays coupled to one of said remote data acquisition units. 32. The method of seismic surveying of Claim 31, wherein said step of selectively obtaining data from at least a portion of said geophone arrays comprises the steps of: communicatively coupling a central control unit to each of said data lines; and selectively addressing each of said remote data acquisition units by communicating a first command signal from said central control unit to each of said remote data acquisition units. 33. The method of seismic surveying of Claim 15, further comprising the step of adjusting parameters of said addressed data from said geophone arrays in response to said monitored shotpoint location.

Inventors: BADGER A S, FREED DENNIS E, HARVEY DONALD W, OLSEN EMIL L, SNOOK JOHN R, BADGER, A., S., FREED, DENNIS, E., HARVEY, DONALD, W., OLSEN, EMIL, L., SNOOK, JOHN, R.
Applicants: GEOSOURCE INC, GEOSOURCE INC.
Application year: 1984
Main classification: G01V1
IPC codes: G01V1