U.S. patent application number 10/237469 was filed with the patent office on 2003-07-10 for seismic data acquisition apparatus and method.
This patent application is currently assigned to Input/Output, Inc.. Invention is credited to Bristow, David, Crews, Gary, Cronan, Robert, Feszthammer, Andras, Iseli, James, Johnson, Allan, Kelly, Charles, Knapp, Greyson, Schumacher, Daniel.
Application Number | 20030128627 10/237469 |
Document ID | / |
Family ID | 23236584 |
Filed Date | 2003-07-10 |
United States Patent
Application |
20030128627 |
Kind Code |
A1 |
Iseli, James ; et
al. |
July 10, 2003 |
Seismic data acquisition apparatus and method
Abstract
The present invention provides a method and apparatus of
acquiring and processing seismic data. One or more controllers are
each coupled to seismic sensors and to each other to form a network
of data acquisition units. A main controller is coupled to a
crossline unit via a cable comprising a synchronizing conductor and
one or more power/data conductors. Commands and data are packaged
such that multiple routings are possible without affecting final
calculations. Each crossline unit is capable of accepting a fiber
optic input, a wire input or a combination.
Inventors: |
Iseli, James; (Allen,
TX) ; Schumacher, Daniel; (Richardson, TX) ;
Bristow, David; (Sugar Land, TX) ; Johnson,
Allan; (Bellville, TX) ; Knapp, Greyson;
(Houston, TX) ; Crews, Gary; (Plano, TX) ;
Kelly, Charles; (Lewisville, TX) ; Cronan,
Robert; (Frisco, TX) ; Feszthammer, Andras;
(Stafford, TX) |
Correspondence
Address: |
PAUL S MADAN
MADAN, MOSSMAN & SRIRAM, PC
2603 AUGUSTA, SUITE 700
HOUSTON
TX
77057-1130
US
|
Assignee: |
Input/Output, Inc.
12300 Parc Crest Drive
Stafford
TX
77477
|
Family ID: |
23236584 |
Appl. No.: |
10/237469 |
Filed: |
September 9, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60318086 |
Sep 7, 2001 |
|
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Current U.S.
Class: |
367/60 |
Current CPC
Class: |
G01V 1/22 20130101 |
Class at
Publication: |
367/60 |
International
Class: |
G01V 001/00 |
Claims
What is claimed is:
1. A seismic data acquisition apparatus comprising: a) a plurality
of sensors for detecting a seismic event, each sensor having an
output indicative of the seismic event; and b) at least one unit
coupled to the plurality of sensors for receiving each sensor
output, the unit adapted to transmit the received outputs as
individual data packets, wherein each data packet includes one or
more characterizing bits.
2. The apparatus of claim 1, wherein the one or more characterizing
bits include information relating to at least one of sensor
location, timing, sensor identification, trace number and record
identification.
3. The apparatus of claim 1, wherein each of the plurality of
sensors is selected from a group consisting of i) accelerometers;
ii) geophones; and iii) hydrophones.
4. The apparatus of claim 1, wherein each of the sensors includes a
MEMS accelerometer.
5. The apparatus of claim 4, wherein each of the sensors further
comprises a three-component MEMS accelerometer package.
6. The apparatus of claim 1 further comprising at least one second
unit coupled to the first unit for receiving the data packets over
a primary route, wherein said at least one second unit includes a
switching device for determining a direction from which the data
packets are transmitted.
7. The apparatus of claim 6, wherein the switching device is
adapted to select a secondary route for receiving said data packets
when said primary route is not available.
8. The apparatus of claim 6, wherein the at least one second unit
includes at least one first port for coupling a low speed route to
the second unit and at least one second input port for coupling a
high speed route to the second unit.
9. The apparatus of claim 6, wherein the primary route includes at
least one of i) an optic fiber and ii) a wire conductor.
10. The apparatus of claim 7, wherein the primary route is an optic
fiber and the secondary route is a wire conductor.
11. The apparatus of claim 7, wherein the primary route is a wire
conductor and the secondary route is an optic fiber.
12. The apparatus of claim 1 further comprising a central
controller for receiving the data packets, said central controller
adapted to determine from said characterizing bits a timing
parameter for storing said received data packets in order.
13. A method of seismic data acquisition, comprising: a) sensing
acoustic energy with a plurality of sensors, each sensor providing
an output indicative of the sensed energy; b) combining the sensor
outputs into a data packet; and c) adding to the data packet one or
more characterizing bits.
14. The apparatus of claim 13, wherein the one or more
characterizing bits include information relating to at least one of
sensor location, timing, sensor identification, trace number and
record identification.
15. The method of claim 13 further comprising wavelength division
multiplexing the data packet.
16. The method of claim 13, wherein the data packet includes a
synchronizing signal and an Ethernet protocol.
17. The method of claim 13, wherein each of the plurality of
sensors is selected from a group consisting of i) accelerometers;
ii) geophones; and iii) hydrophones.
18. The method of claim 13, wherein each of the sensors includes a
MEMS accelerometer.
19. The method of claim 18, wherein each of the sensors further
comprises a three-component MEMS accelerometer package.
20. The method of claim 13 further comprising: a) receiving the
data packets at a unit having a plurality of input ports, said data
packets being transmitted over a primary route; b) determining a
direction from which the data packets are transmitted using a
switching device.
21. The method of claim 20 further comprising selecting a secondary
route for receiving said data packets when said primary route is
not available.
22. The method of claim 20, wherein the unit includes at least one
first port for coupling a low speed route to the unit and at least
one second input port for coupling a high speed route to the
unit.
23. The method of claim 20, wherein the primary route includes at
least one of i) an optic fiber and ii) a wire conductor.
24. The method of claim 21, wherein the primary route is an optic
fiber and the secondary route is a wire conductor.
25. The method of claim 21, wherein the primary route is a wire
conductor and the secondary route is an optic fiber.
26. The method of claim 13 further comprising: a) receiving the
data packets at a central controller; and b) determining from said
characterizing bits a timing parameter for storing said received
data packets in order at the central controller.
27. A deployable field unit for use in a seismic data acquisition
system comprising: a) a housing; b) an input port for receiving a
signal transmitted in a first medium; c) a media converter for
converting said signal for transmission in a second medium; and d)
an output port for transmitted the converted signal.
28. The unit of claim 27, wherein said first medium is one of i) a
wire conductor and ii) an optic fiber.
29. The unit of claim 27, wherein the second medium is one of i) a
wire conductor and ii) an optic fiber.
30. The unit of claim 27, wherein the input port further comprises
a plurality of input ports, the unit further comprising a switching
device for selecting a primary route and a secondary route from
said plurality of input ports.
31. The unit of claim 27, further comprising a circuit in the unit
for determining a first media type of the first medium connected to
the input port and a second media type of the second medium
connected to the output port.
32. A seismic data acquisition system comprising: a) a plurality of
sensors for detecting a seismic event, each sensor having an output
indicative of the seismic event; and b) at least one field unit
coupled to the first plurality of sensors for receiving each sensor
output, the unit adapted to transmit the received outputs as a data
packet, wherein each data packet includes one or more
characterizing bits; and c) a main control and recording unit
coupled to the field unit for receiving the data packets.
33. The system of claim 32, wherein the one or more characterizing
bits include information relating to at least one of sensor
location, timing, sensor identification, trace number and record
identification.
34. The system of claim 32, wherein each of the plurality of
sensors is selected from a group consisting of i) accelerometers;
ii) geophones; and iii) hydrophones.
35. The system of claim 32, wherein each of the sensors includes a
MEMS accelerometer.
36. The system of claim 35, wherein each of the sensors further
comprises a three-component MEMS accelerometer package.
37. The system of claim 32 further comprising at least one second
unit coupled to the first unit for receiving the data packets over
a primary route, wherein said at least one second unit includes a
switching device for determining a direction from which the data
packets are transmitted.
38. The system of claim 37, wherein the switching device is adapted
to select a secondary route for receiving said data packets when
said primary route is not available.
39. The system of claim 37, wherein the at least one second unit
includes at least one first port for coupling a low speed route to
the second unit and at least one second input port for coupling a
high speed route to the second unit.
40. The system of claim 37, wherein the primary route includes at
least one of i) an optic fiber and ii) a wire conductor.
41. The system of claim 38, wherein the primary route is an optic
fiber and the secondary route is a wire conductor.
42. The system of claim 38, wherein the primary route is a wire
conductor and the secondary route is an optic fiber.
43. The system of claim 32 further comprising a central controller
for receiving the data packets, said central controller adapted to
determine from said characterizing bits a timing parameter for
storing said received data packets in order.
44. The system of claim 32 further comprising a conductor coupling
the field unit to the main control and recording unit for
transmitting a synchronizing signal between the field unit and the
central control and recording unit.
45. A method of deploying a seismic data acquisition system
comprising: a) extending a first signal transmission medium over a
first distance; b) coupling the first signal transmission medium to
a field unit; c) extending a second signal transmission medium over
second distance; d) coupling the second signal transmission medium
to a plurality of sensors; e) coupling the first signal
transmission medium to a central control unit.
46. The method of claim 45, wherein the first signal transmission
medium includes a wire conductor for transmitting signals, the
first distance being substantially less than the second distance
and the second signal transmission medium includes an optic
fiber.
47. The method of claim 45, wherein the field unit includes a
plurality of ports for reconfiguring the seismic data acquisition
system to have the second signal coupled to the central controller
and the first signal transmission medium coupled to the plurality
of sensors.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is related to provisional U.S. Patent
Application Serial No. 60/318,086 filed on Sep. 7, 2001 the entire
contents of which are hereby incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates generally to geologic surveys and
more particularly to an apparatus and method for acquiring and
processing seismic data.
[0004] 2. Description of the Related Art
[0005] Conventional geophone and hydrophone systems used in seismic
prospecting typically have several sensors that produce analog
signals indicative of a seismic wave. The seismic wave is usually
produced by an energy source such as a vibrator truck, explosives
or by an air gun in the case of a hydrophone system. These seismic
signals are then conducted to acquisition/conversion circuitry. The
analog signals from one or more remote seismic sensors
(hydrophones, geophones, or other seismic sensors) are sampled and
converted to a series of digital values by the
acquisition/conversion circuitry. The acquisition/conversion
circuitry is typically configurable to, for example, adjust the
sampling rate, alter any digital filtering or other digital signal
processing parameters, or perform diagnostics.
[0006] One or more of these acquisition/conversion circuits are
connected to a data collection unit. Each data collection unit
collects the series of digital values for all the seismic sensors
connected to all the acquisition/conversion units connected to it.
The data collection unit passes that data to a system controller,
usually the truck, which includes a seismic recording device or
Central Recording System ("CRS").
[0007] A conventional system as described above is typically used
in the seismic industry to enable a seismic data acquisition method
called remote digitization. In this method a small number of analog
signals are conveyed by wire to an analog to digital converter
called a "field box" located remotely from the Central Recording
System. In this field box analog signals acquired by the sensors
are converted to digital form. Immediately after the conversion,
digital data are transmitted to the CRS via serial communication.
Typically, a processor and software are used to assign a time slot
for transmitting the data. By example, the box closest to the CRS
is assigned the first time slot and the next box the second time
slot and so forth. A set of digital values from a field box
associated with a particular time slot is called a trace. After all
of the signals are digitized synchronously, each field box
transmits the first trace at the first time. Then the second box
would transmit the data for the first trace in the second time slot
and so forth down the line. After all of the trace data for the
first time slot are transmitted, i.e. time-one samples, then the
process is repeated for another trace from all of the boxes i.e.
time-two samples. In this manner, all of the data from the remote
field units is transmitted to the CRS.
[0008] Early in the development of remote digitization systems the
data were immediately written to tape with all of time-one samples
from all of the traces followed by time-two samples of all the
traces. This method is called multiplexed. In larger systems, the
CRS typically uses the known structure of the data to collect all
of the time samples for one location or trace in sequential memory
or tape location. This organization is called demultiplexed and is
needed by the processing systems that will receive the seismic
data.
[0009] The conventional system has several limitations, especially
as the number of traces in the recording system increase or
redundant methods are needed to improve the reliability of the
system. The order that data arrives at the CRS is used to imply or
calculate the location of the field box sending the data to the
CRS. Using arrival timing in this fashion means that the data
cannot be sent via a route other than the predetermined initial
route. If traces are contaminated during, transmission they must
continue to be passed through the system to preserve the location
so that the CRS can keep track of location. This contaminated data
causes unexpected errors and failures of the system. The system
must add some bits to the data that is transmitted to control the
transmission. Because each data value is sent by itself,
immediately upon acquisition, the overhead becomes very large and
limits the amount of seismic data that can be transmitted over a
single channel.
[0010] Another drawback of the conventional system is the time
required to recover from corrupted or otherwise unusable data
packages transmitted from the data collection units to the main
controller recorder.
[0011] Another drawback of the conventional system is that a system
designer typically must decide to use fiber optic cable or wire
conductor cable to interconnect components regardless of system
length requirements. The typical system component having fiber
optic connectors is prone to failure caused by environmental
conditions and is costly to use for shorter system lengths.
Although copper wire is cost effective at shorter distances, a wire
cable has a limited frequency response over longer distances and is
much more cumbersome to deploy and retrieve.
SUMMARY OF THE INVENTION
[0012] The present invention addresses the above-identified
problems found in the conventional seismic data acquisition system
by providing a system having distributed control over the several
units comprising the system. Additionally, the present invention
provides an apparatus and method for packaging and transmitting
data efficiently and with more reliability.
[0013] One aspect of the present invention provides a seismic data
acquisition apparatus having a plurality of sensors for detecting a
seismic event with each sensor having an output indicative of the
seismic event and at least one control unit coupled to the
plurality of sensors receiving each sensor's output. The unit is
adapted to transmit the received outputs as a data packet and each
data packet includes one or more characterizing bits.
[0014] Another aspect of the present invention provides a seismic
data acquisition system containing a plurality of seismic sensors
for detecting a seismic event with each sensor having an output
indicative of the seismic event. The system includes at least one
field unit coupled to the plurality of sensors receiving each
sensor's output. The unit is adapted to transmit the received
outputs as a data packet with each data packet including one or
more characterizing bits. The seismic data acquisition system
contains a second control unit coupled to the first control unit
for combining data packets received from a plurality of other
control units. A main control and recording unit is coupled to the
second control unit for receiving the combined data packets.
[0015] A third aspect of the present invention is a seismic data
acquisition cable containing a first cable section including wire
connectors coupling a connector at one end of the first cable
section to a circuit at another end of the first cable section,
wherein the circuit is adapted to convert electrical signals to
optical signals. A second cable is coupled to the circuit with the
second cable section including optic fibers.
[0016] A fourth aspect of the present invention is a seismic data
cable containing a first cable section including conductors
coupling a connector at one end of the first cable section to a
circuit at another end of the first cable section wherein the
circuit is adapted to condition electrical signals and to
retransmit the conditioned electrical signals to a second cable
section coupled to a circuit.
[0017] A fifth aspect of the present invention is a method of
seismic data acquisition sensing acoustic energy with a plurality
of sensors with each sensor providing an output indicative of the
sensed energy and combining the sensor outputs into a data packet,
wherein the data packet includes one or more characterizing
bits.
[0018] A sixth aspect of the present invention is a method of
deploying a seismic data acquisition system. The method includes
extending a first signal transmission medium over a first distance,
coupling the first signal transmission medium to a field unit
extending a second signal transmission medium over second distance,
coupling the second signal transmission medium to a plurality of
sensors, and coupling the first signal transmission medium to a
central control unit. The method includes reconfiguring the system
to have the second signal transmission medium coupled to the
central control unit and coupling the first signal transmission
medium to the plurality of sensors. A conductive wire is used as
the signal transmission medium for short distances and an optic
fiber is used for transmitting signals over a long distance. The
reconfiguration is made with the use of a field unit having
multiple ports, a sensing circuit to determine the media type
connected to the unit and a media converter circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The novel features of this invention, as well as the
invention itself, will be best understood from the attached
drawings, taken along with the following description, in which
similar reference characters refer to similar parts, and in
which:
[0020] FIG. 1 is a system schematic of one embodiment of a seismic
data acquisition system according to the present invention;
[0021] FIG. 2 is a schematic showing a coupling arrangement for the
several units of FIG. 1 suited for longer system lengths;
[0022] FIG. 3 is a schematic showing a coupling arrangement for the
several units of FIG. 1 adapted for shorter system lengths;
[0023] FIG. 4 is a diagram of a crossline unit according to the
present invention that allows for the connection of either coupling
arrangement shown in FIGS. 2 and 3;
[0024] FIG. 5 is a flow chart showing a method of system
initialization according to the present invention;
[0025] FIG. 6 is a flow chart showing a method of data acquisition
and conditioning according to the present invention; and
[0026] FIGS. 7A-7B are a flow chart showing a method of data
routing and transmission according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0027] FIG. 1 is a system schematic of one embodiment of a seismic
data acquisition system according to the present invention. The
system 100 includes a primary control and recording unit 102 for
delivering commands to and receiving data signals from other units
in the system 100. As shown, the primary control and recording unit
or central recording system ("CRS") 102 is a mobile unit ("truck").
Alternatively, the primary control and recording unit may be housed
in any vehicle or carrier, or may be permanently or
semi-permanently installed at a predetermined location.
[0028] The primary control and recording unit 102 is coupled to an
intermediate data control unit known as a crossline unit ("XLU")
104. The XLU 104 is coupled to a plurality of data acquisition
units ("DAUs") 106, also referred to herein as "field boxes". As
shown, the couplings 114a and 114b between XLUs 104 provide
redundant transmission paths as will be further described later.
Also shown are redundant transmission paths 110a and 110b between
each DAU group and XLUs to ensure continuous data transmission even
when a primary transmission fails or is otherwise not viable. One
or more sensors 108 are coupled to each DAU 106. The sensors 108
are preferably micromachined micro-electromechanical system
accelerometers referred to as MEMS accelerometers. In a preferred
embodiment, each accelerometer package 108 includes a
three-component MEMS accelerometer sensor having three orthogonal
axes of sensitivity. The sensors, however, may alternatively be any
conventional sensor for sensing acoustic energy waves.
[0029] A sensor 108 detects a seismic event such as an acoustic
wave and converts the acoustic energy into a signal. The signal is
received by an associated DAU 106, which digitizes the signal and
transmits the digital result to the XLU. Signal packets are created
using electronic circuitry preferably housed in the DAU.
[0030] The XLU receives digitized results (packets) from the
plurality of DAU's 106 and combines the several results for
transmission to the CRS 102. Each packet comprises digitized
signals including one or more bits representing the sensed seismic
signal and one or more bits "characterizing bits" for identifying
the transmitted signal. Each characterizing bit includes
information relating to one or more of sensor location, time of
transmission, sensor identification, trace number and record
identification.
[0031] In one embodiment, the sensors 108 are micromachined
accelerometers integrally packaged with a converter thereby
providing a digital output to its associated DAU 106, or directly
to an XLU 104.
[0032] In one embodiment, couplings 112 between the truck and XLU,
and between the XLU and DAUs are cables including one or more
power/data conductors 112a and a synchronizing conductor 112b used
for system timing. The couplings 112 may be any suitable coupling
capable of transferring electrical power and data signals. It is
not necessary that one coupling 112a be the same coupling type as
the other coupling 112b. Exemplary couplings may be any combination
of wire, radio frequency, optical fiber, or electromagnetic.
Furthermore, couplings 112a and 112b might comprise a first signal
(synchronizing signal) riding on a second power and/or data signal
transmitted along a single transmission path or conductor.
[0033] FIGS. 2-4 show a particularly useful embodiment of the
present invention wherein, the XLUs 104 are adapted to sense the
coupling type used and are further adapted to accept wire
conductors, fiber optic conductors or a combination of both to
allow for adapting the system 100 to different length
requirements.
[0034] The connection between XLUs 104 can be either 100 Mb
Ethernet protocol or Gigabit Ethernet protocol. Copper cable may be
used to transmit 100 Mbit Ethernet protocol and optical fiber may
be used to transmit either protocol. Additionally, connection a
synchronization signal is transmitted separate from the Ethernet
signals for copper wire but may be wavelength division multiplexed
to share a fiber with Ethernet.
[0035] Compared to copper cable optical fiber has many desirable
features compared to copper however it also has some drawbacks.
Specifically the features are low loss allowing long transmission
distances, and lightweight easing manual transportation, deployment
and pickup of the cables by the user. The drawbacks of optical
fiber in this environment are associated with the use of optical
connectors. Optical connectors which are required at the cable ends
in a conventional system are sensitive to contamination by dust,
sand, and other foreign materials often encountered in the seismic
field environment. The embodiment shown in FIGS. 2-4 retains the
benefits of using optical fiber while eliminating the use of
problematic optical connector used in the conventional system.
[0036] Referring to FIG. 2. The XLU 104 is connected by a wire
connector 200 to a cable 204. The cable 204 includes a short cable
section 206, typically less than 1 meter, for connecting the XLU
104 to a media converter 202 integrally disposed within the cable
204. The short cable section 206 preferably comprises copper wire
for coupling the XLU 104 to the media converter 202, although any
suitable wire conductor is considered within the scope of this
invention. Within the media converter 202 electrical signals are
converted to optical signals and vice versa using well-known
circuitry. There are no external connectors on the media converter
202 as it is an integral part of the cable 204. Optical fiber is
then used for a major span 208 of the cable 204. The major fiber
optic span 208 supports nominal distances of up to 4 km with
commonly commercially available fiber. Greater distances may be
achieved using specially designed optic fibers. The media converter
eliminates optical connectors in the cable 204. The fiber cable 208
supports either 100 Mbit Ethernet or Gigabit Ethernet.
Additionally, synchronization signal transmission and reception is
supported in the fiber cable through the media converter. These
signals may be transmitted on a single fiber using wavelengths
divisions multiplexing techniques.
[0037] FIG. 3 is a schematic showing a coupling arrangement for the
several units of FIG. 1 adapted for shorter system lengths. For
shorter cable distances, e.g. up to 400 meters, it is desirable to
have a cable comprising only wire conductors, because the
advantages of fiber diminish for shorter cables where weight and
loss are not as important in view of the high cost of fiber cables.
Shown are two XLUs 104 coupled using a cable 300 according to the
present invention. The cable 300 comprises wire conductors 302 and
repeater modules 304. Each repeater module 304 is a bidirectional
device adapted to receive a data package and retransmit the data
package after conditioning the package signal. In a preferred
embodiment, the repeater modules 304 are integrally disposed within
the cable 300 to eliminate the need for external connectors.
Standard 100 Mbit Ethernet will support only cable lengths up to
100 meters with commercially available cable. Thus, the repeater
cable shown in FIG. 3 achieves the 400-meter distance by the
integration of the repeater modules 304 molded within the cable.
These active repeater modules 304 regenerate the signal in both
directions and can achieve a transmission distance of 133 meters
between repeaters and up to 400 meters overall. The copper repeater
cable shown supports a 100 Mbit Ethernet and a synchronization
signal.
[0038] FIG. 4 is a diagram of a crossline unit according to the
present invention that allows for the connection of either coupling
arrangement shown in FIGS. 2 and 3. Connection to the XLU 104 is
made using one or more ports 400. These ports 400 are collectively
referred to as a High Speed Dual Media Port. This port 400 accepts
either of the cable configurations 204 or 300 described above and
shown in FIGS. 2 and 3. Circuits (not separately shown) within the
XLU 104 detects whether a cable is copper repeater cable 300 or
copper/fiber cable 202 and responds accordingly. The detection
circuit may be of the type described in U.S. Provisional
Application serial No. 60/297,354 filed on Jun. 11, 2001, the
specification of which is incorporated herein by reference and
which is assigned to the assignee of this invention. The XLU 104
allows up to 3 simultaneous high speed connections to the unit of
any combination of copper repeater cable and copper/fiber cable. In
this fashion a network of XLU's, DAU's and sensors may be combined
in any needed configuration without the need to specially design
any single component.
[0039] Those skilled in the art would recognize with the benefit of
this disclosure that the apparatus of the present invention might
be practiced in numerous embodiments enabled by this teaching.
Thus, the identification and illustration of XLU's and DAU's as
separate field units should not be construed as a necessary
limitation of this invention. At a conceptual level, the present
invention provides an apparatus for recording seismic data
utilizing a unique data package structure that alleviates the need
for precise timing control for signal transmission. Therefore, any
reference to XLU and/or DAU could be construed as functional
designations within one or more housings or as physical
designations in separate housings. Moreover, the functions of a DAU
could, in part or in whole, be transferred to an XLU.
[0040] The method of the present invention may be practiced using
any of the embodiments described above and shown in FIGS. 1-4. The
method includes power management of the seismic data acquisition
system 100, data packaging and rerouting.
[0041] The primary building block of a method according to the
present invention is a novel paradigm to seismic recording systems
for collecting several time samples of a single location into a
bundle or packet. These packets are large enough that the necessary
information to identify and route the packet is not a significant
factor to the number of bits that must be transmitted. By example,
93% of the bits transmitted using the system of the present
invention are seismic data. These packets are transmitted to the
CRS for recording as they assembled, rather than awaiting a time
slot as with conventional methods. Thus, no assignment of time slot
or master order control across the system is needed. This offers
several advantages. Each packet is transmitted from one field unit
104 to the next field unit 104 of the array. At each location, a
new available packet is added to the string of packets that are
being transmitted, whenever there is time to introduce a new
packet. It is not necessary for there to be a repeated series of
clock pulses to keep all units in synchronization, so packets are
not transmitted simultaneously. Thus, if the clock from the CRS is
lost during the acquisition process a unit can continue to acquire
and transmit data on an internal clock without interfering with
other units or disrupting overall timing.
[0042] This packet approach is not used in conventional systems,
because using a conventional system typically results in
unacceptable loss of several time samples from a single location. A
system according to the present invention increases reliability
over the conventional system by the combined use of several
techniques.
[0043] Before data collection process begins, each field unit 104
is assigned a trace number for a particular record and a record ID
for the seismic event recorded. As each packet is assembled for
transmission, it is given a sequence number that represents the
time of the first sample in the packet. Because the packet may be
lost or corrupted in transmission, the data for each packet is
stored in memory of the DAU. This remote data storage provides a
backup copy of the data in case there are problems with
transmission.
[0044] At substantially the same time that the message is sent to
the field units to assign trace number and record ID, a Field
Equipment Interface (FEI) (software not separately shown) disposed
in the CRS establishes a table in the CRS. This table contains a
matrix of all the packets that are expected for an acquisition.
Additionally, the table contains information about the memory
location that packets are to occupy when they arrive at the CRS. As
each packet arrives, the trace number and sequence number contained
in the packet are examined by the FEI. The packet is "checked off"
in the table and the seismic data is written to the proper location
in the CRS memory. In this manner, the order of packet arrival is
not important to determining the corresponding location of the
sensor that created the data. That information is part of the
packet information. In the same manner, it is possible for the last
time sequence of data to arrive before the first sequence packet.
The sequence number is evaluated by the FEI and is used to control
the memory location of the data storage without affecting other
parts or timing of the system.
[0045] A Cyclic Redundancy Counter (software bits) is added to the
end of each packet. As the packet is passed from unit to unit of
the field equipment the CRC is checked with the data to determine
if there was an error in transmitting the packet. For the exchange
between two units, if there is an error in the transmission a
command is sent to the previous unit to send the packet again. The
data is transmitted from unit to unit in this manner until it
reaches a higher order element that connects line segments. If a
packet is corrupted at this level, there is no adjacent unit to
command retransmission. In this case, the data package block is
simply dropped and not retransmitted. Thus, all packets that are
being handled and passed on by the system are uncorrupted packets.
This method substantially reduces unexpected errors and system
failures caused by corrupted data.
[0046] As the FEI checks off the arrival of data packets, the
matrix is examined for missing packets. The FEI sends a command to
a specific remote unit to retransmit a specified packet based on
its time sequence if a missing packet is detected. Whenever missing
packets cannot be retransmitted successfully, the corresponding
locations in memory are filled with error values. A summary of the
missing packets is sent to a master control unit, which is used to
determine if the record is acceptable.
[0047] Rerouting and retransmission capability enabled by the
system according to the present invention creates the possibility
that packets from one seismic event or record will arrive at the
CRS at the same time as the last packets from the previous event.
Each record or event is assigned a Record ID. This same Record ID
is associated with a unique packet table in the FEI. The FEI keeps
the previous table open during the primary acquisition of the
current table to allow for the late arrival of packets and
retransmission requests. The users of the system set the amount of
time, but it is expected that at least three tables would be
active, i.e. open, at any time.
[0048] In another embodiment of the present invention, test results
from positions that will be used in the future are evaluated in
addition to receiving seismic data from remote units. In seismic
terms, this is called "look ahead testing". This is very difficult
with conventional data transmission methods to include this data
with the seismic data, because it disrupts the order of the data
that is used to determine the location. In the present method, test
results are assigned a different identifier in the packet type. The
status packet can then be transmitted from unit to unit back to the
CRS in the same way that data packets are transmitted. At the FEI
the type is examined and the data and status packets are separated
for different data processing.
[0049] One of the challenges of this method for status messaging is
to tell the source of the message. To address this issue a unique
Status ID is assigned to each unit as it is powered up. Any status
message then contains this Status ID to identify the source of a
status response. A further extension to the status message is
possible now that data and status can be mixed in the same data
stream. This is the idea of an "unsolicited" status or an
"emergency" message. There are several conditions in the system
that require immediate attention. By example the power available
from a battery could have dropped to a level so low that failure
will happen in the next few minutes. In a large system the operator
may not ask for a battery status often enough to measure this
condition. The remote unit is programmed to send an "unsolicited"
status to indicate this error to the CRS. Again the packet of
status is coded so that the FEI recognizes this packet as
unsolicited status and not as a routine response to a query, and
thus treat it as needing immediate attention.
[0050] In another method according to the present invention, a
third type of packet is the "Command" packet. This packet normally
travels from the Central Recording System to the ground units to
control the behavior or parameters of the unit. There are also
unit-to-unit command packets that are sent autonomously by the
field units. These packets contain routing information so that they
can be sent to some units or all units. The command packets are
mixed with the data and status packets and sent by the same network
protocols as the other types of packets. The method allows the
field units and the CRS to quickly determine the type of packet
that is presented and to either reject or act on the packet based
on its type and routing information.
[0051] Networking Methods
[0052] Once the concept of packet organization for sending seismic
data has been established then broader concepts from network theory
can be applied to practical problems and limitations in the
transmission of seismic data and status messages. For brevity, the
term "seismic packet" will be used to mean either or all status,
command or data packets.
[0053] A feature of a seismic system is that all remote digitizer
units sample in unison to an accuracy of 0.25 microseconds or
better across the complete system and that they hold that accuracy
for length of the record. This accuracy is much less than the time
to transmit a signal through wires across the distance of a seismic
recording system. This is further complicated by the potential for
time delays in switches and rerouting of packets. One of the major
limitations of conventional systems using packet transmission and
established communication standards like Ethernet is that timing
information and control is lost.
[0054] In one method according to the present invention, a timing
synchronization signal and the seismic packets are transmitted by
separate dedicated wires or in a single fiber as discussed above.
This allows the use of application-specific protocol and
methodology to distribute the timing signals and at the same time
well established methods and protocols to distribute information
that can be put into packets.
[0055] Using an XLU described above and shown in FIG. 4 according
to the present invention, it is possible to plug any of the
connectors into the unit in any order. One connector would be for
cable toward the CRS and one away. The third connector would be
used to make a redundant connection to a third node or cross line
unit. It is very easy with this third connection to make networks
that are very complex with many routes between two nodes. Therefore
it is possible that any packet whether it is data or command could
arrive at the same location from two different directions and at
slightly different times. Network theory is used to control data
management. A class of devices known as managed switches are used
to determine the direction from which data are coming and where the
data are to go. A managed switch may be, and is preferably a
software solution managed within a particular unit such as an XLU.
This is covered under the general class of Ethernet messaging
protocol that is used by the system. A managed switch keeps a list
of which port is generating information. If that unit appears in
the "to" part of the message the switch sends the data to that
port. Secondly, the switch sends out network messages to establish
the health of the network. If there are two ways for a packet to
get to the same node or cross line unit, one of the links is
deliberately disabled. The managed switches continue to poll the
network on a periodic basis. If links or units fail, the network is
readjusted and the messages are sent by a different route. In this
manner, a link can fail and the seismic crew can continue to record
while repairs are made.
[0056] For a seismic system, it is not enough to reroute the
seismic packets as the managed switch does. It is likely that a
link has failed because the cable between the ground units has
failed. For a seismic system, this also means that the all
important synchronization signal is lost. The units can continue
for a short time on internal clocks, but the master clocks are
needed for long-term synchronization of the system. It is necessary
then that the switches not only redirect the seismic data, but also
establish new timing control paths. There is also the need to
update the time adjustment for the different route, because the
length and number of nodes will be different and cause different
delays. In this invention, the information from the health message
of the standard protocol is used to make the decisions on switching
the timing control path. By this method, the timing control is
provided with a redundant path for reliability with automatic
switching of the route enabled by the method of using the data
network performance to switch the synchronization signal.
[0057] Another networking embodiment of the present invention is
the automatic adding of units to the network. The XLUs and DAUs are
constantly sending network messages looking for new units. When a
new unit responds it is attached to the network and the user
display in the CRS shows the unit to be available for use to
collect seismic data.
[0058] An exemplary data-handling method according to the present
invention is shown in FIGS. 5-7. FIG. 5 is a flow of system
initiation commands, FIG. 6 is a flow of data acquisition and FIG.
7 is a flow of data packet routing. The method is preferably
conducted in part using using a set of instructions stored on a
readable medium such as magnetic disc or memory device in a unit
such as the DAU described above and shown in FIGS. 1-4.
[0059] According to one embodiment of a method according to the
present invention, seismic data acquisition is initiated as shown
in FIG. 5. A user initiates a request to record seismic data.
Typically the user is a field operator at the central truck
recorder. The user selects which DAU field units are to be active
for the record associated with the seismic data to be acquired.
These selections are preferably performed by entering the
selections into a computer console at the truck. Once the
selections are entered, a command is sent via typical telemetry to
the active DAU's 106. A field equipment interface unit housed in
the CRS 102 provides interface between the CRS and field
equipment.
[0060] A table is created describing the active traces, and the
table is transmitted to the field equipment interface. The field
equipment interface expands the table into a table of expected
packets. The field equipment interface then prepares to receive
packets from DAUs.
[0061] The user selects a time to start recording using the truck
console, and a command is issued to the DAUs to assign a time and
record identification to packets as characterizing bits.
[0062] Referring now to FIG. 6, a data acquisition method according
to the present invention begins with sensors providing output
signals indicative of a seismic event to activated field units. The
DAU field units convert the analog signals to digital signals and
the digital signal is placed into a memory device within the field
unit.
[0063] The stored data is then transferred to a buffer memory as an
output data packet. The data packet is then completed by adding
characterizing bits, i.e. an identification header is attached
which includes a record identification, a trace identification and
a sequence number. The data packet with characterizing bit is then
transmitted via the telemetry network.
[0064] FIGS. 7A-7B are a flow chart to show a data packet routing
method according to the present invention. Status packets and data
packets are combined on a networked seismic data acquisition system
and the packets are the network using Ethernet addresses. All
packets are routed to the field equipment interface, and the field
equipment interface is used to determine whether the arriving
packet is a status packet or a data packet. Status packets are
transmitted to an output display in the CRS for display to the
user.
[0065] When the field equipment interface determines that an
arriving packet is a seismic data packet, then an associated table
for proper identification is selected and a "received" bit flag is
set in the table based on the trace identification and packet
sequence information contained in the packet characterizing bits.
The format of the seismic data in the packet is converted and
removed from the packet in order and written to memory in time and
trace order.
[0066] After a predetermined time elapses, the table of received
packets is examined for missing packets. If the table shows one or
more missing packets, then commands are sent to DAUs to recover
missing data from the DAU memory and retransmit the data
package.
[0067] The retransmitted data package is treated in the same manner
as the original data packages. The field equipment interface
determines that an arriving packet is a seismic data packet, then
an associated table for proper identification is selected and a
"received" bit flag is set in the table based on the trace
identification and packet sequence information contained in the
packet characterizing bits. Unrecoverable data package information
is assigned a predetermined value to complete the records at the
central recorder.
[0068] The foregoing description is directed to particular
embodiments of the present invention for the purpose of
illustration and explanation. It will be apparent, however, to one
skilled in the art that many modifications and changes to the
embodiment set forth above are possible without departing from the
scope and the spirit of the invention. It is intended that the
following claims be interpreted to embrace all such modifications
and changes.
* * * * *