EP2059835A2 - Wireless systems and methods for seismic data acquisition - Google Patents

Abstract

Systems and methods for acquiring seismic data are described, one system comprising one or more vibrators, one or more base stations, a land seismic data recording station, and a sensor system for acquiring and/or monitoring land-seismic sensor data, the sensor system comprising a plurality of sensor modules each comprising a seismic sensor, wherein the seismic sensors transmit at least a portion of the data to the one or more base stations which in turn transmit at least some data they receive to the recording station, and wherein all communication between the vibrators, base stations, recording station, and seismic sensors is completely wireless.

Description

WIRELESS SYSTEMS AND METHODS FOR SEISMIC DATA ACQUISITION Cross-reference to Related Applications [0001] The present application claims priority under 35 U.S.C. § 119(e) to United States Provisional Application serial number 60/844,633, filed September 14, 2006, and also claims priority under 35 U.S.C. § 120 to United States Non-Provisional Patent Application serial number 11/683,883, filed March 8, 2007, (14.0331) both of which are incorporated by reference herein in their entireties. Background of the Invention 1. Field of Invention [0002] The present invention relates to the field of seismic data acquisition systems and methods of using same. More specifically, the invention relates to systems and methods for efficiently gathering seismic data during a land-based seismic survey. 2. Related Art [0003] Land seismic acquisition aims to capture the acoustic and elastic energy that has propagated through the subsurface. This energy may be generated by one or more surface sources such as vibratory sources (vibrators). The vibrators produce a pressure signal that propagates through the earth into the various subsurface layers. Here elastic waves are formed through interaction with the geologic structure in the subsurface layers. Elastic waves are characterized by a change in local stress in the subsurface layers and a particle displacement, which is essentially in the same plane as the wavefront. Acoustic and elastic waves are also known as pressure and shear waves. Acoustic and elastic waves are collectively referred to as the seismic wavefield. [0004] The structure in the subsurface may be characterized by physical parameters such as density, compressibility, and porosity. A change in the value of these parameters is referred to as an acoustic or elastic contrast and may be indicative of a change in subsurface layers, which may contain hydrocarbons. When an acoustic or elastic wave encounters an acoustic or elastic contrast, some part of the waves will be reflected back to the surface and another part of the wave will be transmitted into deeper parts of the subsurface. The elastic waves that reach the land surface may be measured by motion sensors (measuring displacement, velocity, or acceleration, such as 1 geophones, accelerometers, and the like) located on the land The measurement of elastic

2 waves at the land surface may be used to create a detailed image of the subsurface

3 including a quantitative evaluation of the physical properties such as density,

4 compressibility, porosity, etc This is achieved by appropriate processing of the seismic

5 data

6 [0005] Seismic sensor units typically also contain the electronics needed to

7 digitize and record the seismic data In one known embodiment, each sensor unit is

8 connected to a land seismic cable, which is connected via cables to a recording

9 instrument on a surface vehicle or other surface facility such as a platform The land

10 seismic cable provides electric power and the means for transferring the recorded and

11 digitized seismic signals to the recording instrument Land seismic is a vital part of

12 secunng both the discovery and efficient production of hydrocarbons However, as

13 currently practiced today, land seismic requires an extensive use of cables to connect a

14 network of sensors to produce an image of underlying layers of the ground Activities

15 related to cables such as transportation, laying and rolling may include up to 50% of the

16 total logistic activities Furthermore cables and connectors may account for over 30% of

17 the total cost of the ground equipment Problems related to cables and connectors such as

18 shorts, opens and intermittent problems may reduce the effective acquisition time up to

19 50% Cables may introduce safety risks to field crews, other human beings and animals,

20 and may damage the environment by leaving operational footprint And finally cables

21 may limit the freedom of laying the sensors in new and unconventional patterns

22 [0006] There have been efforts to reduce the use of cables in performing land

23 seismic Wireless land seismic systems and methods are discussed for example in U S

24 Pat Nos 7,124,028, 6,219,620, and 6,070,129 In some known embodiments, radio

25 frequency signals are used to transfer seismic data from multiple geophones to an

26 intermediate collecting node, which then transfers the collected data to a central control

27 station via radio frequency wireless, cables, or optical fiber In more recent

28 embodiments, such as discussed in the '028 patent, a collecting node is not used, rather,

29 the geophones include components enabling short-range radio communication between

30 geophones in hop-to-hop communication

31 [0007] U S published application number 20060247505 discloses a sensor

32 system, particularly for medical uses, which allows sensor data to be monitored from any

33 remote location The emphasis is on providing users, typically a medical patient, the opportunity to be mobile, rather than having to stay at home or other single location, such as a hospital room Both a user of the sensor system and an external entity may monitor the sensor data, and a communication link between the user and emergency personnel can be provided The sensor system comprises a sensor module having a sensor and a first wireless link that wirelessly transmits data sampled from the sensor to a mobile communication device (such as a cell phone or personal digital assistant PDA), the mobile communication device having a second wireless link that receives the data from the sensor module and wirelessly transmits the data to a server The first wireless link may comprise a wireless communication protocol chosen from the group of a radio frequency communication protocol, a magnetic induction protocol, and a wireless personal area network protocol (WPAN) The second wireless link may comprise a wireless communication protocol chosen from the group of GSM standard, GPRS, GPS, 3G, WIFI (801 11), WiMAX, and a radio frequency communication protocol In discussing problems of previously known medical monitoring systems, the inventor mentions that similar drawbacks are also applicable to other data acquisition systems, such as environmental monitoring systems, and seismic monitoring systems, however there is no further disclosure, teaching, or suggestion of seismic sensor systems or seismic data acquisition Mobile wireless technology has acquired a status separate from wireless data networking, as evidenced, for example by their separate treatment in references such as the Network Dictionary (see for example the discussion of wireless data networking at http //www netwoikdictionarv com/wirelessΛViielessDataNetworking php and its separate treatment of mobile wireless) [0008] Although there has been some use of wireless data transmission in the land-seismic data acquisition field, there remains room for improvement in the areas of robustness, scalability, cost, and power-efficiency The present invention is devoted to addressing one or more of these areas

Summary of the Invention [0009] In accordance with the present invention, wireless systems and methods for land-seismic data acquisition are described which reduce or overcome short- comings of previously known wireless systems and methods in terms of one or more of robustness, scalability, cost, and power-efficiency Systems and methods of the invention allow more efficient land-seismic data acquisition, for example 3-D and 4-D land seismic data acquisition, such as during exploration for underground hydrocarbon-bearing reservoirs, or monitoring existing reservoirs. Electromagnetic signals may be used to transfer data to and/or from the sensor units, to transmit power, and/or to receive instructions to operate the sensor units. [0010] A first aspect of the invention is a land seismic data acquisition system comprising: one or more vibrators, one or more base stations, a seismic data recording station, and a sensor system for acquiring and/or monitoring land-seismic sensor data and transmitting the data to the one or more base stations, the sensor system comprising a plurality of sensor modules each comprising a seismic sensor, wherein all communication between the vibrators, base stations, recording station, and seismic sensors is completely wireless. Systems of the invention may be characterized as comprising a wireless data network, wherein the wireless data network comprises the seismic sensors transmitting at least a portion of the data to the one or more base stations via first wireless links which in turn transmit at least some data they receive to the recording station via second wireless links, as further explained herein. Also as further explained herein, the recording station need not be on land, and need not be immobile. For example, the recording station may be selected from a stationary land vehicle, a moving land vehicle, a stationary marine vessel, a moving marine vessel, and a moving airborne vessel, such as a helicopter, dirigible, or airplane. [0011] As used herein the term "completely wireless" means there are no wired, fiber (including optical fiber) or other physical communication connections between individual sensor units, between individual vibrators, between individual base stations, between any sensor unit and base stations, between any sensor unit and the data recording station, between the any sensor unit and any vibrator, between any vibrator and the data recording station, between any vibrator and any base station, and the like. This does not, however, rule out the possibility of physical connections, for example between two vibrators in the same vibration area. [0012] The base stations may be located strategically to cover predefined groups of sensor modules as further illustrated herein. In these embodiments, each group of sensor modules may relay data wirelessly via a mesh topology and/or in a hop to hop fashion (also referred to herein as multi hopping) Star topologies and other topologies may also be used, but mesh topology will produce the greatest redundancy Between each base station and the data recording station (for example recording truck), seismic data may be transferred directly from base station to recording station Sensor modules may be spaced relatively close together in systems of the invention, for example a distance ranging from 1 meter up to about 10 meters Because of the relatively short distance between sensor modules, multi-hopping may circumvent the potential wireless communication (RF, microwave, infra-red) problems in uneven terrain, or terrain including man-made obstacles It is known that for transmitting data wirelessly between points A and B separated by a large distance, relaying between multiple spots between A and B will consume less energy compared to direct wireless communication between points A and B [0013] Systems within the invention include those comprising a first wireless link that wirelessly transmits seismic data sampled from a seismic sensor to a base station (which may be a mobile or non-mobile communication device), the base station having a second wireless link that receives the seismic data from the sensor modules and wirelessly transmits the seismic data to the land seismic data recording station, the one or more vibrators having a third wireless link that receives commands from the land seismic data recording station and wirelessly transmits vibrator data (such as status information) to the land seismic data recording station As used herein the term "mobile", when used to describe a device, includes hand-held devices and devices that may be worn on the body of a person, for example on a belt, in a pocket, in a purse, and the like It is not meant to include objects that may in fact be moved, but only with great effort, such as a building or shed, or with less effort a desk top computer [0014] In certain system embodiments the first wireless link may be selected from any wireless personal area network (WPAN) communication protocol The second and third wireless links may be individually selected from any wireless communication protocol that supports point to multi point (PMP) broadband wireless access These protocols may include, but are not limited to IEEE standard 802 16 (sometimes referred to as the WiMax (Worldwide Interoperability for Microwave Access) standard), IEEE standard 80220, and the like The second and third wireless links may use the same or different protocols [0015] Certain land seismic data acquisition systems of the invention may utilize wireless links and equipment allowing broadcasting of messages (audio, video, alphanumeric, digital, analog, and combinations thereof) between sensor modules, vibrators, base stations, and the recording station, or simply between the sensor modules The messages may be time tagged and used for distance measure and clock calibration The communication network may also be used for transmission of status information and/or quality control (QC) [0016] A second aspect of the invention comprises methods of acquiring land seismic data, including time-lapse land seismic data acquisition, one method comprising

a) wirelessly initiating one or more vibrators from a recording station, the vibrators producing one or more vibratory signals through a land area, b) measuring reflected land-seismic data using a sensor system positioned on the land area, the sensor system comprising a plurality of sensor modules each comprising a seismic sensor, c) wirelessly transmitting at least some of the seismic data from the plurality of sensor modules to one or more base stations, d) wirelessly transmitting at least some data received by the one or more base stations to a recording station, and e) optionally repeating steps (a) through (d) [0017] Other methods of the invention include passive listening surveys (where no vibratory source is used) and electromagnetic (EM) surveys, where one or more of the sensor units comprises one or more EM sensors [0018] As used herein, "survey" refers to a single continuous period of seismic data acquisition (which may occur simultaneously, sequentially, or with some degree of time overlap), over a defined survey area, multiple surveys means a survey repeated over the same or a same portion of a survey area but separated in time (time- lapse) In the context of the present invention a single seismic survey may also refer to a defined period of seismic acquisition in which no controlled seismic sources are active (which also may be referred to alternatively as passive seismic listening or micro seismic measurements) [0019] Systems and methods of using systems of the invention allow more efficient land data acquisition (including time lapse) than previously known systems and methods These and other features will become more apparent upon review of the brief description of the drawings, the detailed description of the invention, and the claims that follow Brief Description of the Drawings [0020] The manner in which the objectives of the invention and other desirable characteristics may be obtained is explained in the following description and attached drawings in which [0021] FIG 1 illustrates a simplified plan view of a system of the invention, [0022] FIG 2 illustrates schematically wireless communication between components of systems of the invention, and [0023] FIGS 3-4 illustrate schematically prior art communication topologies useful in practicing system sand methods of the invention [0024] It is to be noted, however, that the appended drawings are not to scale and illustrate only typical embodiments of this mvention, and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments Detailed Description [0025] In the following description, numerous details are set forth to provide an understanding of the present invention However, it will be understood by those skilled in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible [0026] The present invention relates to completely wireless systems and methods of using the inventive systems in land seismic data acquisition A primary feature of the invention is the substantial elimination of all wires, cables, and fibers for communication between vibrators, seismic sensors, base stations, and the recording station This does not rule out the use of wires, cables, or fibers (such as optical fibers) for example in the recording station equipment and vibrators, for example for power, and the use of tie down cables if necessary in windy conditions [0027] The wireless systems and methods of the invention are improvements over systems and methods that use wire or optical fiber for communications in terms of one or more of robustness, scalability, cost, and power-efficiency Systems and methods of the invention allow more efficient land seismic data acquisition, for example 3-D and 4-D land seismic data acquisition, such as during exploration for underground hydrocarbon-bearing reservoirs, or monitoring existing reservoirs. Electromagnetic signals may be used to transfer data to and/or from the sensor units, to transmit power, and/or to receive instructions to operate the sensor units. [0028] A simplified schematic view of a land seismic data acquisition system of the invention is illustrated in FIG. 1. An area 2 to be surveyed, may have physical impediments to direct wireless communication between, for example, a recording station 14 (which may be a recording truck) and a vibrator 4a. A plurality of vibrators 4a, 4b, 4c, 4d may be employed, as well as a plurality of sensor unit grids 6a, 6b, 6c, 6d, 6e, and 6f, each of which may have a plurality of sensor units 8. As illustrated in FIG. 1, for example approximately 24-28 sensor units 8 may be placed in the general vicinity around a base station 10. The number of sensor units 8 associated with each base station 10 may vary widely according to the goals of the survey number, however, due to the architecture of the communications between the various components (discussed herein, particularly with reference to FIGS. 3 and 4), the number should be less than required in previously known systems. Circles 12 indicate the approximate range of reception for each base station 10. This range may be the same or different for each base station. [0029] The system illustrated in FIG. 1, using the plurality of sensor units 8, may be employed in acquiring and/or monitoring land-seismic sensor data for area 2, and transmitting the data to the one or more base stations 10. All communications between vibrators 4, base stations 10, recording station 14, and seismic sensors 8 are completely wireless, as that term is defined herein. Alternatively, systems of the invention may be described as comprising a wireless data network, for example as illustrated schematically in FIG. 2, wherein the wireless data network comprises multiple seismic sensors 8 transmitting at least a portion of the seismic data they sense to the one or more base stations 10 via first wireless links 9, which in turn transmit at least some data they receive to the recording station 14 via second wireless links 16. Commands may be sent from recording station 14 to vibrators 4 via wireless links 18, and, to the extent data is exchanged between vibrators 4 and recording station 14, wireless links 18 may also be considered part of the wireless data network. [0030] First wireless links 9 may be characterized as Wireless Personal- Area Networks (WPAN). A "WPAN" is a personal area network (PAN) using wireless connections. WPAN is currently used for communication among devices such as telephones, computers and their accessories, as well as personal digital assistants, within a short range. The reach of a PAN is typically within about 10 meters. These protocols may include, but are not limited to Bluetooth (registered certification mark of Bluetooth SIG, Inc., Bellevue Washington), ZigBee (registered certification mark of ZigBee Alliance Corporation, San Ramon, California), Ultra-wideband (UWB), IrDA (a service mark of Infrared Data Association Corporation, Walnut Creek, California, HomeRF (registered trademark of HomeRF Working Group Unincorporated Association California, San Francisco, California), and the like. Bluetooth is the most widely used technology for the WPAN communication. Each technology is optimized for specific usage, applications, or domains. Although in some respects, certain technologies might be viewed as competing in the WPAN space, they are often complementary to each other. [0031] The IEEE 802.15 Working Groups is the organization to define the WPAN technologies. In addition to the 802.15.1 based on the Bluetooth technology, IEEE proposed two additional categories of WPAN in 802.15: the low rate 802.15.4 (TG4, also known as ZigBee) and the high rate 802.15.3 (TG3, also known as Ultra- wideband or UWB). The TG4 ZigBee provides data speeds of 20 Kbps or 250 Kbps, for home control type of low power and low cost solutions. The TG3 UWB supports data speeds ranging from 20 Mbps to lGbps, for multi-media applications. In the Table 1, the main characters of the WPAN technologies as specified in the IEEE 802.15 are delineated.

Table 1. Wireless Personal Area Network Characteristics

* From networkdictionary.com, accessed at: http://www.networkdictionarv.com/wirelebs/WP AN.php?PHPSESSID=354101 c49bc9d97659791 acaecddc aJ6, on November 8, 2006 [0032] In wired communication systems, mesh network topology is one of the key network architectures in which devices are connected with many redundant interconnections between network nodes such as routers and switches. (See definition of mesh topology in the networkdictionary.com) In a wired communication system using mesh topology, if any cable or node fails, there are many other ways for two nodes to communicate. While ease of troubleshooting and increased reliability are definite pluses, wired mesh networks are expensive to install because they use a lot of cabling. Often, a mesh topology will be used in a wired communication system in conjunction with other topologies (such as Star, Ring and Bus) to form a hybrid topology. Some WAN architecture, such as the Internet, employ mesh routing. Therefore the Internet allows sites to communicate even during a war. [0033] There are two types of mesh topologies: full mesh (as depicted in FIG. 3) and partial mesh (as depicted in FIG. 4). Full mesh topology occurs when every node has a circuit connecting it to every other node in a network. In wired networks, full mesh is very expensive to implement but yields the greatest amount of redundancy, so in the event that one of those nodes fails, network traffic can be directed to any of the other nodes Full mesh is usually reserved for backbone networks With partial mesh, some nodes are organized in a full mesh scheme but others are only connected to one or two in the network Partial mesh topology is commonly found in peripheral networks connected to a full meshed backbone It is typically less expensive to implement and yields less redundancy than full mesh topology [0034] In systems and methods of the invention, due to the wireless nature of the communications using a wireless data network architecture, redundancy, robustness, and flexibility, are all increased, while cost as reduced As illustrated in the full mesh topology of FIG 3, sensors 8a-8h may communicate wirelessly directly with each other sensor through multiple direct wireless links 20 In other embodiments, for example as illustrated in the partial mesh topology of FIG 4, sensor 8a may communicate wirelessly directly with only sensors 8b, 8c and 8g via wireless communications 20, and indirectly with sensors 8d, 8e, 8f, and 8h though wireless communication links 22 [0035] The second and third wireless links (i e , links 16 and 18, respectively, as illustrated in FIG 2) may be individually selected from any wireless communication protocol that supports point to multi-point (PMP) broadband wireless access These protocols may include, but are not limited to IEEE standard 802 16 (sometimes referred to as the WiMax (Worldwide Interoperability for Microwave Access) standard), IEEE standard 802 20, and the like The IEEE wireless standard presently has a range of up to 30 miles (48km), and presently can deliver broadband at around 75 megabits per second, although the invention is not so limited This is theoretically, 20 times faster than a commercially available wireless broadband See for example the discussion in http //www tutoual-iepoits com/wireless/wimax/tutoπal php, which is the reference for the discussion which follows [0036] The IEEE 802 16 WiMax standard was published in March 2002 and provided updated information on the Metropolitan Area Network (MAN) technology The extension given in the March 2002 publication extended the line-of-sight fixed wireless MAN standard, focused solely on a spectrum from 10 GHz to 60+ GHz This extension provides for non line of sight access in low frequency bands like 2 - 11 GHz These bands are sometimes unlicensed This also boosts the maximum distance from 31 to 50 miles (50 to 80km) and supports PMP (point to multipoint) and mesh technologies The IEEE approved the 802 16 standards in June 2004 WiMax may be used for wireless networking like the popular WiFi. WiMax, a second-generation protocol, allows higher data rates over longer distances, efficient use of bandwidth, and avoids interference almost to a minimum. WiMax can be termed partially a successor to the Wi-Fi protocol, which is measured in feet, and works over shorter distances. [0037] As used in the context of seismic data acquisition in systems of the invention, the seismic sensors and base stations may be compared to a metropolitan area networking (MAN), as given in the 802.16 standard, sometimes referred to as fixed wireless. In fixed wireless, a backbone of base stations is connected to a public network. As with a MAN, each of base station 10 supports many "fixed subscriber stations" (sensor units 8), which are akin to either public WiFi hot spots or fire walled enterprise networks. Base stations 10 use a media access control (MAC) layer, and allocate uplink and downlink bandwidth to "subscribers" (sensor units 8) as per their individual needs. This is basically on a real-time need basis. The MAC layer is a common interface that makes networks interoperable. In the future, one can look forward to 802.11 hotspots, hosted by 802.16 MANs. These would serve as wireless local area networks (LANs) and would serve the end users directly too. [0038] WiMax has two main topologies, either of which may be used in systems and methods of the present invention, namely Point to Point for backhaul and Point to Multi Point Base station for Subscriber station. In each of these situations, multiple input multiple output antennas may be used. The protocol structure of IEEE 802.16 Broadband wireless MAN standard is illustrated in FIG. 5. FIG. 5 (from Javvin.Com) shows four layers: convergence, MAC, transmission and physical. These layers map to two of the lowest layers, physical and data link layers of the OSI model. [0039] Use of WiMax protocol provides systems and methods of the invention and their end users many user applications and interfaces, for example Ethernet, TDM, ATM, IP, and VLAN. The IEEE 802.16 standard is versatile enough to accommodate time division multiplexing (TDM) or frequency division duplexing (FDD) deployments and also allows for both full and half-duplex terminals. [0040] IEEE 802.16 supports three physical layers. The mandatory physical mode is 256-point FFT OFDM (Orthogonal Frequency Division Multiplexing). The other modes are Single carrier (SC) and 2048 OFDMA (Orthogonal Frequency Division Multiplexing Access) modes. The corresponding European standard - the ETSI Hiperman standard defines a single PHY mode identical to the 256 OFDM modes in the 802.16d standard. [0041] The MAC was developed for a point-to-multipoint wireless access environment and can accommodate protocols like ATM, Ethernet and IP (Internet Protocol). The MAC frame structure dynamic uplink and downlink profiles of terminals as per the link conditions. This entails a trade-off between capacity and real-time robustness. The MAC uses a protocol data unit of variable length, which increases the standards efficiency. Multiple MAC protocol data unit may be sent as a single physical stream to save overload. Also, multiple Service data units (SDU) may be sent together to save on MAC header overhead. By fragmenting, large volumes of data (SDUs) may be transmitted across frame boundaries and may guarantee a QoS (Quality of Service) of competing services. The MAC uses a self-correcting bandwidth request scheme to avoid overhead and acknowledgement delays. In systems and methods of the invention, this feature may also allows better QoS handling than previously known systems and methods. The terminals have a variety of options to request for bandwidth depending on the QoS and other parameters. The signal requirement can be polled or a request can be piggybacked. [0042] In systems and methods of the invention, the 802.16 MAC protocol may perform Periodic and Aperiodic activities. Fast activities (periodic) like scheduling, packing, fragmentation and ARQ may be hard-pressed for time and may have hard tight deadlines. They must be performed within a single frame. The slow activities, on the other hand, may execute as per pre-fixed timers, but are not associated with any timers. They also do not have specific time frame or deadline. [0043] Table 2 compares similarities and differences in the first wireless and second and third wireless links useable in systems and methods of the invention (borrowed from Javvin.Com).

Table 2. Comparable Properties of First and Second Wireless Links

[0044] The 802.11 is based on a distributed architecture, whereas, WiMax is based on a centrally controlled architecture. In this the scheduler residing in the Base station (BS) has control of the wireless media access. WiMax can support multiple connections conforming to a set of QoS parameters and provides the packet classifier ability to map the connections to many user applications and interfaces. [0045] Certain embodiments of systems and methods of the invention may use a wireless data network based on a newer protocol, IEEE 802.20. This standard, like the 802.16 standard, is aimed at wireless high-speed connectivity to mobile consumer devices like cellular phones, PDAs and laptop computers. The IEEE 802.20 Mobile Broadband Wireless Access Working Group is developing an air-interface standard for mobile BWA systems that operate in licensed bands below 3.5 GHz. It is targeting peak data rates of over 1 Mb/s per user at vehicular speeds to 250 km/hour. This maybe useful for systems of the invention using, for example, a moving data recoding stations, for example a moving truck, an airplane or helicopter, rather than a stationary recording station. Systems and methods using this standard will operate in the 500 MHz - 3.5 GHz range. Currently, this protocol is offered by QUALCOMM Flarion Technologies, Bedminster, New Jersey, and ArrayComm, San Jose, California. [0046] Systems and methods of the invention may include provision of multi- antenna signal processing (MAS) software architectures for implementation of the second and/or third wireless links employing WiMAX. The WiMAX profiles support both adaptive antenna system (AAS) and multiple-input/multiple-output (MIMO) architectures in baseline form. MAS implementation, such as though use of the product known under the trade designation "A-MAS" from ArrayComm, may enhance baseline MIMO through the addition of essential interference mitigation. Generic MIMO systems provide link robustness and enhance point-to-point data rates by transmitting signals multiple times and/or transmitting multiple signals. Without active interference mitigation, these additional transmissions incur the cost of decreased signal-to- interference ratios for co-channel users in other cells. In the single-cell environments typified by wireless LANs, where MIMO techniques have seen their first commercial success, this increased interference has no adverse effects. In a networked system such as WiMAX where multiple cells share the same spectral resources, the increased interference degrades network capacity and overall service quality, even though it may improve links for some users. It also prevents the use of MIMO techniques for enhancing data rates outside the cell center. By combining AAS techniques with MIMO in our A-MAS solution, MIMO's benefits can be realized throughout the cells in the network, simplifying network planning and providing performance improvements operators can rely on. A-MAS software may run as a synthesizable core or as an embedded DSP code within common ASIC architectures, integrating into client device physical layers through modular interfaces. The approach taken by software products such a that known as A- MAS takes precise control of the space dimension and puts radio energy (or receive sensitivity) only where it's really required. The software drives an array of two or more antennas on either the client device, the base station, or both, leveraging the principle of coherent combinations of radio waves to create a focus of transmit energy (or receive sensitivity) on the intended recipient (sender) and the absence of energy (sensitivity) on sources of co-channel interference. As applied in the context of inventive methods and systems, A-MAS-enabled base stations and sensor units may take advantage of all the possible gains from using multiple antennas: link budget improvements from diversity and combining gains, along with client data rate and overall network capacity benefits from active interference mitigation and spatial mutliplexing. [0047] Systems and methods of the present invention solve or reduce problems associated with cable-based land seismic systems, or previously known sensor unit-based systems for acquisition of time-lapse land seismic data, namely cost, power and data transfer. [0048] Land sensor units useable in the invention may include, in addition to measurement sensors, a high-precision clock, low-power electronics, long-term battery and memory components, and an autonomous power generating unit which provides power to charge the batteries in the sensor units without being reliant on power charge from external means. [0049] The sensor units may remain on the land between seismic surveys or be removed therefrom. During idle periods, an autonomous power generation component, if present, will generate enough power to recharge the autonomous power source, which may be one or more rechargeable batteries, one or more capacitors, and the like. Batteries and capacitors may be based on any chemistry as long as they are self-sufficient for the duration intended, which may be months to years. Batteries or battery cells such as those known under the trade designation "Li-ion VL45E", available from SAFT, Bagnolet, France, may be used. Another alternative is to use capacitors as storage devices for power. Capacitors are smaller and have higher storage capacity, such as discussed in the publication "Researchers fired up over new battery", MIT News Office, February 8, 2006, accessed November 7, 2006 at http://web.mit.edu/newsoffice/2006/batteries-0208.html, incorporated herein by reference. Furthermore, sensor units of the invention may be placed in "sleep" mode for energy conservation during periods of no operation. [0050] "Autonomous power generation" components are to be distinguished from "autonomous power sources." As used herein, the phrase "autonomous power generation" is an optional, but highly desirable feature for sensor units of the invention, and refer to one or more components allowing the autonomous power source or sources to be regenerated, recharged, or replenished, either fully or partially, in order that the seismic sensor unit may remain on the land between seismic surveys. While in theory this may be possible through power brought to the seismic sensor unit by means of a vehicle, this is a slow and cumbersome process. Instead, the sensor units of the present invention may include a means of extracting power from their local environment, sometimes referred to as energy harvesting. Examples of suitable autonomous power generation components include those which may use wind energy, solar energy, and the like, which may be transformed into electrical energy by known means of energy conversion. The autonomous power sources (batteries, for example) may be recharged during periods between seismic surveys which could be anywhere between a few months and one to two years. [0051] Sensors useable in the invention may be individual sensors or a package of two or more sensors. One suitable sensor package is that known under the trade designation "4C Sensor" available from WesternGeco LLC, comprised of three geophones or accelerometers. [0052] Sensor units useable in the invention may also comprise an electronics module having ultra-low power requirements, and may include a high-precision clock, an analog-to-digital converter, power management software and hardware, and a control module for data input/output. [0053] The total power consumption of the digitizing electronics within a sensor unit may be expected to not exceed 50mWatt. In addition, by using low-power memory (for example flash EPROM), the total power consumption of the complete inventive sensor units is not expected to exceed 15OmW at any time. This is at least a factor of 10 less than with current technology used in land sensor units. The battery capacity that is needed to provide power to an inventive sensor unit for a typical seismic survey period of six weeks is only 150Wh. Rechargeable Li- Ion batteries may provide approximately 350Wh/l and 15OWbAg, hence the total battery volume and weight is expected approximately 0.41iter and 0.6kg. [0054] Data that is recorded by the land sensor units may be transferred to the base stations, an din turn to the recording station. In other embodiments it may be desirable to remove and transport one or more memory modules from a particular sensor unit. For example, one might equip a sensor unit with N memory modules for N surveys. In these embodiments, for example, for each survey one memory module is taken out. Both methods of data transfer may be used. In certain embodiments data transfer may be achieved through multiple channels and/or by multiple methods in order to increase the speed and/or amount of the data transmission. [0055] Methods of using systems of the invention may include measurement, calculation and other sub-systems useful in implementing methods of the invention. Calculation units may include software and hardware allowing the implementation of one or more equations, algorithms and operations as required, as well as access databases, data warehouses and the like, via wire or wireless transmission. [0056] The initial position to within few meters of accuracy of one or more sensor units of the invention may be determined for instance by using GPS. [0057] It is within the invention to interface systems of the invention with other data acquisition systems and methods of land seismic data acquisition, such as cable-based systems, and systems using previously known land seismic systems. As one non-limiting example, where a reliable land cable has been operating successfully, one might use that land cable and its sensors, and position sensor units in a grid on one or both sides of the cable [0058] In certain embodiments, regardless of the environment or survey area, a higher density of land sensor units throughout the spread may improve overall operational efficiency by decreasing the distances between the sensor units and the associated degradation of wireless signals The shape of the sensor units or grids of sensor units is not m itself relevant [0059] Although only a few exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims In the claims, no clauses are intended to be in the means-plus- function format allowed by 35 U S C § 112, paragraph 6 unless "means for" is explicitly recited together with an associated function "Means for" clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures

Claims

What is claimed is

1. A system comprising:

one or more vibrators, one or more base stations, a land seismic data recording station, and a sensor system for acquiring and/or monitoring land-seismic sensor data, the sensor system comprising a plurality of sensor modules each comprising a seismic sensor, wherein the seismic sensors transmit at least a portion of the data to the one or more base stations which in turn transmit at least some data they receive to the recording station, and wherein all communication between the vibrators, base stations, recording station, and seismic sensors is completely wireless.

2. The system of claim 1 wherein the one or more base stations are located strategically to receive the seismic data from corresponding one or more groups of sensor modules.

3. The system of claim 2 wherein at least one group of sensor modules relays at least some of the seismic data wirelessly within the group from sensor module to sensor module via a communication topology selected from a partial mesh topology, a mesh topology, and a star topology.

4. The system of claim 3 wherein at least one group of sensor modules relays data packets wirelessly within the group from sensor module to sensor module via multi- hopping.

5. The system of claim 1 wherein between each base station and the data recording station the data is transferred directly from the base station to the recording station.

6. The system of claim 1 wherein the sensor modules are spaced a distance ranging from about 1 meter up to about 10 meters.

7. The system of claim 1 comprising a first wireless link that wirelessly transmits the seismic data obtained by one or more of the seismic sensors to the base station, the base station comprising a second wireless link that receives the seismic data from the one or more seismic sensors and wirelessly transmits the seismic data to the land seismic data recording station..

8. The system of claim 7 wherein the one or more vibrators comprises a third wireless link that receives commands from the land seismic data recording station and wirelessly transmits vibrator data to the land seismic data recording station..

9. The systems of claim 1 wherein the base station is selected from mobile and non-mobile communication devices.

10. The system of claim 7 wherein the first wireless link is selected from wireless personal area network (WPAN) communication protocols.

11. The system of claim 10 wherein the personal area network (WPAN) communication protocols are independently selected from protocols covered by IEEE standard 802.15.

12. The system of claim 8 wherein the second and third wireless links are independently selected from wireless communication protocols that support point to multi-point (PMP) broadband wireless access.

13. The system of claim 12 wherein the wireless communication protocols that support point to multi-point broadband wireless access are independently selected from IEEE standard 802.16 and IEEE standard 802.20.

14. A land seismic data acquisition system comprising: one or more vibrators, one or more base stations, a land seismic data recording station, and a sensor system for acquiring and/or monitoring land-seismic sensor data, the sensor system comprising a plurality of sensor modules each comprising a seismic sensor, and a wireless data network, wherein the wireless data network comprises the seismic sensors transmitting at least a portion of the data to the one or more base stations via first wireless links which in turn transmit at least some data they receive to the recording station via second wireless links.

15. The system of claim 14 wherein the first wireless links have frequency bands selected from 2.4 - 2.48GHz, 868MHz, and 902 - 928MHz, and wherein the first wireless links have maximum data transfer rates of 20Kbps @ 868MHz, 40 Kbps @ 902 - 928 MHz, and 250Kbps @ 2.4 - 2.49GHz.

16. The system of claim 15 wherein the first wireless links have range of about 100 meters.

17. The system of claim 16 wherein the second wireless link has frequency band selected from 500MHz - 3.5GHz and 2 - 1 IGHz, maximum data transfer rate of 70Mbps @ 2 - 1 IGHz, and a range of about 31 miles (50km).

18. A method comprising: a) wirelessly initiating one or more vibrators from a recording station, the vibrators producing one or more vibratory signals through a land area; b) measuring reflected land-seismic data using a sensor system positioned on the land area, the sensor system comprising a plurality of sensor modules each comprising a seismic sensor; c) wirelessly transmitting at least some of the seismic data from the plurality of sensor modules to one or more base stations; d) wirelessly transmitting at least some data received by the one or more base stations to a recording station; and e) optionally repeating steps (a) through (d).

19. The method of claim 18 comprising repeating steps a) through d) and performing time-lapse seismic data acquisition.

20. The method of claim 18 wherein step c) comprises wirelessly transmitting at least some of the seismic data from the plurality of sensor modules to one or more base stations using first wireless links having frequency bands selected from 2.4 - 2.48GHz, 868MHz, and 902 - 928MHz, the first wireless links having maximum data transfer rates of 20Kbps @ 868MHz, 40 Kbps @ 902 - 928 MHz, and 250Kbps @ 2.4 - 2.49GHz, the first wireless links having range of about 100 meters, and wherein step d) comprises wirelessly transmitting at least some data received by the one or more base stations to a recording station using a second wireless link having frequency band selected from 500MHz - 3.5GHz and 2 - 1 IGHz, maximum data transfer rate of 70Mbps @ 2 - 1 IGHz, and a range of about 31 miles (50km).