WO2009039488A1

WO2009039488A1 - Autonomous underwater vehicle used to calibrate a long baseline navigation network

Info

Publication number: WO2009039488A1
Application number: PCT/US2008/077206
Authority: WO
Inventors: Christopher Von Alt
Original assignee: Hydroid, Inc.
Priority date: 2007-09-21
Filing date: 2008-09-22
Publication date: 2009-03-26

Abstract

An AUV adapted for the calibration of a deployed long baseline navigation network is discussed. The AUV may be configured to calibrate a previously established long baseline navigation network in which transponders have drifted from their original deployed locations. The AUV may also deploy the long baseline navigation network being calibrated.

Description

AUTONOMOUS UNDERWATER VEHICLE

USED TO CALIBRATE A LONG BASELINE NAVIGATION NETWORK

Related Applications

The present application claims priority to, and the benefit of, U.S. Provisional Patent Application, Serial No. 60/974,334, filed September 21, 2007.

Field of the Invention

The embodiments of the present invention relate generally to Autonomous Underwater Vehicles (AUVs), and more specifically to an AUV adapted for and used in calibrating a long baseline navigation network.

Background

An AUV is a robotic, unmanned submersible device that is driven through the water by a propulsion system, controlled and piloted by an onboard computer, and maneuverable in three dimensions to follow precise preprogrammed trajectories. The AUVs may operate completely autonomously. Alternatively, the AUVs may communicate with a surface vessel, such as a ship. The AUVs are usually battery, rechargeable battery or fuel cell powered, and may be deployed for a variety of underwater missions. The AUVs may travel at variable speed and depth under water. The AUVs are pre-programmed to perform a variety of underwater tasks and frequently engage in these tasks with little or no ongoing communication with human or computerized operators on the water surface. Sensors onboard and attached to the AUV sample the ocean as the AUV moves through it, providing the ability to make both spatial and time series measurements. Sensor data collected by an AUV is automatically geospatially and temporally referenced and normally of superior quality.

AUVs are frequently used by the oil and gas industries for mapping the seafloor. The detailed maps generated by the AUVs based on the collected data are used for building subsea infrastructures in a cost effective manner with the minimum disruption to the environment. Among other missions, the AUVs may also be used to map an area for mine detection or to study the ocean or the ocean floor.

Additional types of tasks that may be performed by an AUV include data collection and underwater site monitoring and vary greatly depending upon the size of the AUV and the types of equipment with which the AUV is outfitted. For example, smaller AUVs are usually deployed in shallower waters for their missions while larger AUVs which have the ability to descend to greater depths are used for deep water missions. In order for an AUV to perform its assigned tasks, the AUV must be able to map any collected data to the location of the AUV at the time the data is collected. The mapping of data to a location requires the AUV to be able to ascertain its position at all times. One of the techniques that may be used to allow the AUV to ascertain its current position is to have the AUV utilize a long baseline navigation network that has been deployed in the underwater environment in which it is operating. A long baseline navigation network includes multiple transponders deployed in an array structure or other pattern on the ocean floor.

Brief Summary

Embodiments of the present invention provide an AUV adapted for calibrating a previously deployed long baseline navigation network in which transponders have moved from their original deployed locations. The embodiments may also use an AUV to deploy and calibrate a new long baseline navigation network. The AUV may be pre- programmed prior to its mission with patterns for deploying the transponders needed for a long baseline navigation network, may receive instructions after launch, or may automatically deploy the transponders based upon detected conditions in the underwater environment.

In one embodiment of the present invention, an Autonomous Underwater

Vehicle (AUV) apparatus includes a communication apparatus, at least one instrument package, a long baseline navigation network calibration module and navigation software. The communication apparatus is able to receive a Global Positioning Satellite (GPS) signal when the AUV is in a surfaced position. The instrument package includes acoustic sonar equipment used to send signals to, and receive signals from, multiple transponders in a deployed long baseline navigation network. The long baseline navigation network calibration module is used to calibrate the deployed long baseline navigation network by identifying current positions for the transponders. The identifying is based on a received GPS signal and an analysis of sonar signals sent to, and received from, multiple transponders. The long baseline navigation network calibration module calibrates the long baseline navigation network by updating a record of a location of at least one of the transponders within the long baseline navigation network to reflect its identified current position. The navigation software is subsequently used to determine a current location of the AUV using the calibrated long baseline navigation network.

In another embodiment of the present invention, a method for calibrating a long baseline navigation network using an Autonomous Underwater Vehicle (AUV) includes receiving a Global Positioning Satellite (GPS) signal when the AUV is in a surfaced position. A recorded position for each of multiple transponders forming a deployed long baseline navigation network is identified within a record stored in the AUV. At least one acoustic sonar signal is sent from the AUV to the vicinity of the recorded position for at least one of the transponders. The AUV receives at least one acoustic sonar signal from at least one of the transponders in reply to the sent signal. The received signal(s) include(s) identifying information uniquely identifying the replying transponder. The method also includes calibrating in the AUV the long baseline navigation network with a long baseline navigation network calibration module. The calibrating identifies a current position for the replying transponder. The identifying is based on the received GPS signal and an analysis of the acoustic sonar signals sent to, and received from, the replying transponder. The long baseline navigation network calibration module updates the record of the location of the replying transponder within the long baseline navigation network to reflect its identified current position. The method further includes subsequently determining with navigation software a current location of an AUV using the calibrated long baseline navigation network. Brief Description of the Drawings

Embodiments of the invention are pointed out with particularity in the appended claims. The advantages of the invention described above, as well as further advantages of the invention, may be better understood by reference to the following description taken in conjunction with the accompanying drawings, in which:

Figure 1 depicts an exemplary underwater environment in which an AUV may calibrate or deploy and calibrate a long baseline navigation network; Figure 2A depicts an exemplary long baseline navigation network including intelligent transponders that communicate with each other and relay information to an AUV upon being queried by the AUV;

Figure 2B depicts an exemplary long baseline navigation network including intelligent transponders that communicate with each other and relay information to an AUV without the AUV querying the transponders;

Figure 3 depicts an exemplary underwater environment in which two AUVs communicate with each other and the transponders;

Figure 4 depicts an exemplary AUV adapted for deploying and/or calibrating a long baseline navigation network; Figure 5 is a flowchart of an exemplary sequence of steps that may be followed by an embodiment of the present invention to calibrate an existing long baseline navigation network; and

Figure 6 is a flowchart of an additional exemplary sequence of steps that may be followed by an embodiment of the present invention to use an AUV to deploy and calibrate a new long baseline navigation network.

Detailed Description

Saltwater, and to a lesser extent fresh water, interferes with many types of electromagnetic radiation such as Global Positioning Satellite (GPS) signals. As a result, an ocean environment presents navigational challenges for the AUVs as it is not practical for the AUVs to repeatedly return to the surface to take GPS measurements in order to verify their location. The constant travel to and from the surface would deplete battery life and unacceptably shorten mission duration. As a result, conventionally, AUVs have used long baseline navigation networks that were previously deployed by surface vessels to identify their location while submerged. A long baseline navigation network includes a series of transponders, usually fixed to but resting some height above the ocean floor. The transponders are deployed from the surface at a predetermined location. When transponders are deployed, they normally include an anchor, which lands on the seafloor, an anchor line which connects the transponder to the anchor on the seafloor and a floatation mechanism which is either attached to, or contained in, the transponder. The floatation mechanism forces the transponder to rise off the sea- floor and the anchor line stops the transponder from rising and holds it at the desired elevation above the sea-floor. Once they have been deployed, the transponders may be queried by the AUVs acoustic sonar instruments in order to identify the AUVs current position. The response time from the transponders may be measured and a current position for the AUV may be calculated based upon the determined proximity of the AUV to the transponders.

Unfortunately, there is a problem with relying on a previously established long baseline navigation network in order identify a position for an AUV during an operation. The transponders forming the long baseline navigation network are initially deployed to pre-determined locations. However, the deployed transponders drift with currents in an unpredictable manner while dropping to the sea floor after initial deployment. After the transponder/anchor/float system is released at the surface it falls to the seafloor. In the deep ocean this can take up to 60 minutes or more. While falling, unknown currents and drag forces acting on the transponder system causes it to drift horizontally in an unpredictable manner. As a result, the transponders final resting position is not known with enough certainty to permit it to be used as a navigation reference for many applications. This uncertainty in the actual location of the transponder adversely affects the mapping of the data collected by an AUV. The mapped location for the collected data will not match to the exact location where it was collected if the actual location of the transponder differs from the approximate location of the transponder that was recorded when the transponder was deployed from the surface. The embodiments of the present invention allow an AUV to calibrate a long baseline navigation network on an as needed basis for a specific mission. The long baseline navigation network may have been previously deployed by a surface vessel. Alternatively, the long baseline navigation network may be established and calibrated by an AUV deploying the transponders. For example, the AUV may set up its own long baseline navigation network for a specific location such as an oil field. When calibrating a long baseline navigation network, the AUV can account for any movement of the transponders that occurred after release from the surface. As used in this application, calibration of a long baseline navigation network refers to identifying and recording an accurate current location of each transponder in a long baseline navigation network.

The transponders in the long baseline navigation network are deployed in a pattern. According to the embodiments of the present invention, the transponders may be queried by one or more AUVs. For example, the transponders may be queried using acoustic sonar instruments. An AUV may send one or more sonar signals to a transponder. A transponder replies by sending a unique identification acoustic signal back to the AUV. The signals sent by the transponders are not limited to identification signals and may include additional information. For example, an intelligent transponder may send signals indicating its depth or distance from another transponder, etc. The length of time it takes the transponder' s response to reach the AUV may be measured. A current position for the transponder may be calculated by the AUV based upon the AUVs current position and an analysis of the sonar data. The process of determining the transponders position is discussed further below.

Figure 1 depicts an exemplary underwater environment in which an AUV may calibrate or deploy and calibrate a long baseline navigation network. An AUV 100 is depicted in an underwater environment. A surface vessel may have deployed transponders 120, 122, 124 and 126 to form a long baseline navigation network. Subsequently, the AUV 100 that has been programmed with the original locations of the transponders 120, 122, 124 and 126 is released in the vicinity of the long baseline navigation network. Prior to descent, the AUV 100 may determine its location by obtaining a GPS reading. While on the surface, the AUV 100 may use sonar to identify the previously deployed transponders and sonar ranges to establish their respective present locations. The AUV 100 may send multiple sonar signals to the last known location of a transponder to be able to estimate the transponder' s location using one or more algorithms, such as a triangulation algorithm. For example, the AUV 100 may send three or more separate requests from three or more different locations to a transponder 126 and then compute the current location of the transponder 126 based on the three or more replies to the request.

In an exemplary embodiment, to determine the actual transponder locations, the AUV 100 navigates to a location near a transponder. While on the surface taking a GPS reading, the AUV 100 interrogates the transponder and receives a signal from the transponder indicative of the range to the transponder. The AUV 100 then moves to another position and repeats the process. For example, the AUV 100 may move to a position rotated 90 or 120 degrees from the approximate location of the transponder, take another GPS reading and repeat the sonar interrogation of the transponder. The approximate location of the transponder rests at the center of a circle or other pattern with a diameter that is large enough to ensure that unique range measurements are obtained. It will be appreciated by those skilled in the art that the size of the circle or other pattern will depend upon many factors. The AUV 100 may navigate the entire circle or pattern while on the surface obtaining ranges and GPS readings as it goes. Alternatively, the AUV 100 may reduce the number of locations (e.g.: four at 90 degrees or 3 at 120 degrees, etc.). This process is repeated for each transponder in the deployed long baseline navigation network. The use of a triangulation algorithm is for illustrative purposes only and should not be construed as limiting. One of ordinary skill in the art will appreciate that many other algorithms or approaches may be used to calculate the location, i.e. the coordinates, of a point using multiple data points.

A calibration module in the navigation software on the AUV 100 calibrates the long baseline navigation network to determine and account for the amount the respective transponders may have changed location because of ocean currents and other factors while falling to the seafloor or after being in place on the ocean floor for a period of time. Once the transponder's location has been identified the AUV 100 updates its position in the recorded network and moves on to the next transponder. For example, in Figure 1, transponders 120, 122, 124 and 126 may have originally been deployed in an equidistant manner and subsequently one transponder 124 moved a little while one transponder 126 moved significantly from its original location. The embodiments of the present invention enable these changes to transponder location to be identified and accounted for in order to calibrate the long baseline navigation network. One of skill in the art will appreciate that the array illustrated in Figure 1 is for illustrative purposes and should not be construed as limiting. The transponders may be deployed to form many types of patterns. The transponders may further be deployed at variable depths. For example, transponder 120 may be placed at a deeper level than the transponder 122 either intentionally or due to the surface irregularities of the ocean floor.

Alternatively, in one embodiment, the AUV 100 may self-deploy the transponders 120, 122, 124 and 126 to establish the long baseline navigation network. The AUV 100 may obtain a GPS reading while surfaced and then deploy transponders 120, 122, 124 and 126 in a pre-determined pattern. The pattern in which the transponders are deployed may be related to the tasks the AUV 100 is conducting. For example, the transponders may be deployed in a pattern that allows a prospective oil field to be surveyed.

However, even when the transponders are deployed by an AUV that intends to use the long baseline navigation network, the network must still be calibrated to identify the transponder's actual location. An AUV allows transponders to be deployed from a greater depth than when they are deployed from a surface vehicle. Even so, the transponders may not reach the ocean floor at the exact location where they were initially deployed. Thus, it is still necessary to calibrate the long baseline navigation network with the AUV upon deployment of the transponders by the AUV.

AUVs utilized in the embodiments of the present invention may be programmed with a best guess about each transponder's initial location in the baseline navigation network. They may be programmed prior to launch or after beginning their mission. While AUVs frequently operate with no communication with an operator after launch, in some circumstances bi-directional communication may occur and the AUVs may operate in a semi-autonomous manner. The AUV may take a GPS reading on the water surface above the approximate location of a transponder. After receiving the transponder's response signals, the calibration module on the AUV may execute an algorithm that uses information derived from the length of time that the response signals took to reach the AUV and corresponding location of the AUV based on GPS readings in order to determine each transponder's current location. The AUV may then travel to another transponder's approximate location and repeat the survey.

Once the long baseline navigation network formed from the transponders 120, 122, 124 and 126 has been calibrated, the AUV 100 knows the accurate location of the transponders and can collect data and map the data accurately to the actual location from which the data was gathered using its onboard navigation software. It should be appreciated that the long baseline navigation network may include different numbers of transponders, and the embodiments of the present invention are not restricted to the use of long baseline navigation networks that employ exactly four transponders as illustrated in Figure 1.

According to an exemplary embodiment of the present invention, the transponders may be "intelligent" transponders that are able to do more than merely provide identifying information. The information sent out by an intelligent transponder may include other types of information, in addition to identification data, including but not limited to information about the transponder' s depth, and/or the distance between the transponder and other transponders.

Intelligent transponders may communicate with each other. For example, as illustrated in Figure 2A, in response to a query from an AUV, a first intelligent transponder 222 may communicate with a second intelligent transponder 224, for example, to collect identification information from the second intelligent transponder 224. The first intelligent transponder 222 may also record the length of time it took for the response to reach it from the second intelligent transponder. The response information may be used to determine how far away the second intelligent transponder 224 is from the first intelligent transponder 222. It will be appreciated that intelligent transponders may also gather information from non-intelligent transponders. After collecting information from the second transponder 224, the first transponder 222 may send the identification information of the first and second transponders to the AUV 200 along with any other gathered information in a single communication in response to a request from the AUV 200. Accordingly, the AUV 200 may more quickly collect the information about the long baseline navigation network needed for the calibration process. This is especially important in long baseline navigation networks including many transponders. By providing the identification information of several transponders in a single communication along with information that can be used to determine location, (i.e. information allowing the calculation of distance between transponders), the calibration of the long baseline navigation network can be performed more quickly which may result in an extension of the time available for the AUV to perform its mission. It should also be appreciated that transponder-to- transponder communication is not limited to communication between two transponders and that any number of transponders may communicate with each other. Alternatively, the first intelligent transponder 222 may also send the identification information and additional information for both the first and second transponders to the AUV 200 without the AUV 200 first querying the first or second transponders individually, as illustrated in Figure 2B.

According to another exemplary embodiment of the present invention, the long baseline navigation network may be calibrated (or deployed and calibrated) using multiple AUVs. Once the long baseline navigation network is calibrated, the multiple AUVs may be used to conduct multiple vehicle surveys to increase productivity, to insure adequate temporal and spatial sampling, and to otherwise efficiently perform the many types of AUV missions. As illustrated in Figure 3, a first AUV 300 may deploy the transponders 320 and 322. The first AUV 300 may also gather information from transponders 320 and 322 to locate the transponders 320 and 322. Similarly, a second AUV 305 may deploy the transponders 324 and 326. The second AUV 305 may also gather information from transponders 324 and 326 to locate the transponders 324 and 326. AUVs 300 and 305 may share the information about the location of the transponders 320, 322, 324 and 326 when calibrating the long baseline navigation network. According to an exemplary embodiment, the transponders 320, 322, 324 and 326 may be intelligent transponders. Alternatively, the AUVs 300 and 305 illustrated in Figure 3 may each have a different purpose. For example, AUV 300 may deploy the transponders 320, 322, 324 and 326. Upon deployment of the transponders, AUV 305 may gather location information for the transponders 320, 322, 324 and 326 to calibrate the long baseline navigation network. The AUVs 300 and 305 may work in parallel. For example, after AUV 300 deploys transponder 320, AUV 305 may gather the location information for transponder 320. Thus, the calibration of the long baseline navigation network may be completed in less time.

According to yet another exemplary embodiment, AUV 300 that is on the water surface may gather GPS information at pre-determined intervals and convey this information to AUV 305 that is submerged. This way, it is possible to use multiple GPS readings in calibrating the long baseline navigation network with increased precision while preventing the AUV 305 from traveling all the distance to the water surface to gather the GPS reading. One of ordinary skill in the art will appreciate that AUV-to- AUV communication is not limited to communication between two AUVs and that any number of AUVs may communicate with each other.

Figure 4 depicts an exemplary AUV adapted for calibrating and/or deploying and calibrating a long baseline navigation network. The AUV 100 is equipped with navigation software 400 that is used to calculate the current position of the AUV 100 once the long baseline navigation network has been calibrated. The navigation software 400 also includes a long baseline navigation network calibration / deployment module 410 that is used to calibrate (or deploy and calibrate) a long baseline navigation network by identifying (or deploying and identifying) transponders' locations in a deployed long baseline navigation network. In one embodiment, the AUV 100 may be equipped with internal transponder storage with a deployment mechanism 420 or external transponder storage with an accompanying deployment mechanism 430. The internal transponder storage 420 provides an internal location where the transponders may be stored prior to deployment. Similarly, the external transponder storage 430 provides an external location where the transponders may be secured to the exterior of the AUV 100 prior to deployment. The long baseline navigation network calibration/deployment module 410 is in communication with the respective internal and/or external deployment mechanisms 420 and 430 and automatically sends a deployment signal when the navigation software 400 determines that the AUV 100 has reached a proper position from which to deploy the transponders.

The AUV 100 also includes an instrument package 440 that includes sonar equipment. In one embodiment, the instrument package 440 includes side- scan sonar instruments. It will be appreciated that other detection/measuring instruments may also be used in combination with, or in place of, the side-scan sonar. For example, the instrument package 440 may also include a towed-array sonar. The sonar equipment is used to send sonar signals to, and receive signals from, the transponders 120, 122, 124 and 126 to identify the location of the transponders within the long baseline navigation network during calibration and to identify the location of the AUV with reference to the transponders during the mission. The AUV 100 also includes communication apparatus 450 that includes a GPS link that allows the AUV 100 to obtain a GPS reading on its location when the AUV 100 is surfaced. As discussed above, the GPS reading is subsequently used to calibrate the long baseline navigation network.

The navigation software 400 and the long baseline navigation network calibration / deployment module 410 may be one or more separate applications, plug- ins, processes or other forms of executing software code providing the functionality described herein. Although described as integrated into the navigation software 400, it will be appreciated that the long baseline navigation network calibration / deployment module 410 may also be separate from, but communicating with, the navigation software 400. It should also be appreciated that the functionality described herein for the navigation software 400 and the long baseline navigation network calibration / deployment module 410 may also be divided over a number of different executable software processes that collectively provide the functionality described herein.

It will be appreciated that in fields such as oil/gas/mineral exploration and data gathering/environmental monitoring, the fact that one or more AUVs may deploy and calibrate their own long baseline navigation network represents significant time and resource savings. Similarly, in areas which include previously deployed transponders, the embodiments of the present invention enable one or more AUVs to calibrate the long baseline navigation network and then use the previously deployed network to make accurate location determinations by accounting for transponder drift.

Figure 5 is a flowchart of an exemplary sequence of steps that may be followed by an embodiment of the present invention to calibrate an existing long baseline navigation network. The sequence begins with the original deployment of transponders from a surface vessel in a pattern designed to form a long baseline navigation network (step 500). The identity of each transponder and the location at which it was deployed is recorded. Subsequently, at a later time ranging anywhere from minutes to months or years later, the AUV 100 is launched from the surface (i.e. from a vessel, dock, etc) (step 510). When in the vicinity of the location from which at least one of the transponders were originally deployed, and while still on the surface, the AUV takes a GPS reading to confirm its location (step 520). The AUV 100 then sends out a sonar requests to the vicinity of the recorded location of one or more of the deployed transponders (step 530). As described above a series of GPS readings and sonar requests may be taken for each transponder with the AUV changing locations between each GPS reading and request. Upon locating a first transponder, the AUV 100 may travel to a location on the ocean surface that is recorded as being in the vicinity of a second transponder to take readings to locate the second transponder. The process iterates with the AUV sending out sonar requests to the suspected location of each of the deployed transponders. If the transponders were deployed in an area of swift current, or if a lengthy period of time has passed, the transponders may have drifted from their original deployed location. Once all of the responses have been received from the transponders, the calibration software on the AUV 100 may determine that no transponder drift has occurred and therefore no changes are necessary for the originally recorded locations of the transponders (step 540). Alternatively, the calibration software in the AUV 100 may determine that one or more transponders have changed location and accordingly will adjust the location of the transponder or transponders in the long baseline navigation network (step 540). If the AUV 100 determines that a transponder has changed location, the AUV 100 then calibrates the long baseline navigation network by updating the recorded positions of the transponders in the long baseline navigation network to reflect the present transponder locations revealed in their respective responses to the sonar query (step 550). Once the actual locations of the transponders in the long baseline navigation network have been ascertained, the AUV 100 may operate in the area using the long baseline navigational network to verify location so that acquired data may be mapped correctly against the location at which it was obtained (step 560).

The embodiments of the present invention may also enable an AUV 100 to self- deploy and calibrate a long baseline navigation network. Figure 6 is a flowchart of an additional exemplary sequence of steps that may be followed by an embodiment of the present invention to use an AUV to deploy and calibrate a long baseline navigation network. The sequence begins with the launch of the AUV 100 from the surface (step 600). The AUV 100 may then deploy the transponders to establish the long baseline navigation network (step 610). The AUV 100 may deploy the transponders from the surface, while descending or while at an operating depth. Even at an operating depth closer to the ocean floor, the transponders may drift before hitting the ocean floor due to the underwater environmental effects. Thus, it may be necessary for the AUV to calibrate the long baseline navigation network by identifying the actual location of the transponders using the techniques provided above. The pattern of deployment of the transponders may be programmed into the AUV 100 before launch, may be received via a communication after launch, or may be determined programmatic ally based upon dynamically detected conditions. For example, while taking sensor reading, the AUV 100 may detect an area representing a possible mineral deposit on the ocean floor. In response to the sensor reading, the calibration/deployment module 410 may issue a command to establish a long baseline navigation network so that extensive mapping of the possible mineral find may take place.

Following the deployment of the transponders, the AUV returns to the surface and takes a GPS reading to confirm its location (step 620). The calibration/ deployment module 410 in the navigation software 400 then calibrates the long baseline navigation network by identifying actual transponder locations as described above to take into account drifts that may have occurred upon deployment of the transponders (step 630). Once the software has calibrated the network, the AUV 100 may operate in the area using the long baseline navigational network to verify its location so that acquired data may be mapped correctly against the location at which it was obtained (step 640). In an alternative embodiment, the sonar mapping of the transponder locations occurs while the AUV 100 is submerged. In this alternative embodiment, the calibration process works as described above except that the calibration module and/or navigation software calculate an offset to the GPS reading that allows the GPS coordinates that were gathered on the surface to be relied upon after descent. For example, the AUV 100 takes a GPS reading on the surface. Software on board the AUV tracks the speed, heading, time and other factors during descent from the surface and updates in real-time the AUVs location by plotting an offset to the original GPS location. This offset location is then used when the sonar mapping described above occurs while the AUV is submerged. This embodiment allows the AUV to perform the sonar mapping/calibration of the long baseline network while closer to the transponders (thus allowing more accurate readings) and/or the calibration to occur when the AUV is closer to its mission area.

It should be appreciated that although several examples herein have referred to the "ocean", the AUV 100 described herein may be used in many different underwater environments, including but not limited to, oceans, rivers, lakes, ponds and other underwater bodies.

Since certain changes may be made without departing from the scope of the present invention, it is intended that all matter contained in the above description or shown in the accompanying drawings be interpreted as illustrative and not in a literal sense. Practitioners of the art will realize that the sequence of steps and architectures depicted in the figures may be altered without departing from the scope of the present invention and that the illustrations contained herein are singular examples of a multitude of possible depictions of the present invention.

Claims

We Claim:

1. An Autonomous Underwater Vehicle (AUV) apparatus comprising: communication apparatus, the communication apparatus able to receive a Global Positioning Satellite (GPS) signal when the AUV is in a surfaced position; at least one instrument package, the instrument package including acoustic sonar equipment used to send signals to, and receive signals from, a plurality of transponders in a deployed long baseline navigation network; a long baseline navigation network calibration module used to calibrate the deployed long baseline navigation network by identifying current positions for the plurality of transponders, the identifying based on a received GPS signal and an analysis of sonar signals sent to, and received from, the plurality of transponders, the long baseline navigation network calibration module calibrating the long baseline navigation network by updating a record of a location of at least one of the plurality of transponders within the long baseline navigation network to reflect the identified current position of the at least one of the plurality of transponders; and navigation software, the navigation software determining subsequently a current location of the AUV using the calibrated long baseline navigation network.

2. The apparatus of claim 1 wherein the calibrating of the long baseline navigation network is performed using at least two AUVs.

3. The apparatus of claim 1 wherein at least one of the plurality of transponders is an intelligent transponder able to provide information in addition to identifying information in response to a sonar signal sent from the AUV.

4. The apparatus of claim 3 wherein the intelligent transponder provides current depth information for the intelligent transponder to the AUV and the long baseline navigation network calibration module uses the depth in calibrating the long baseline navigation network.

5. The apparatus of claim 3 wherein the intelligent transponder provides information relating to its distance from at least one of the plurality of transponders in the long baseline navigation network to the AUV and the long baseline navigation network calibration module uses the distance information in calibrating the long baseline navigation network.

6. The apparatus of claim 3 wherein the intelligent transponder provides information relating to its distance from each of the plurality of transponders in the long baseline navigation network to the AUV and the long baseline navigation network calibration module uses the distance information in calibrating the long baseline navigation network.

7. The apparatus of claim 3 wherein the intelligent transponder provides the additional information to the AUV in response to a query received from the AUV.

8. The apparatus of claim 3 wherein the intelligent transponder provides the additional information to the AUV by initiating communication with the AUV.

9. The apparatus of claim 1 wherein the sonar data indicates at least one of the plurality of transponders has moved from a previously recorded position.

10. The apparatus of claim 1, further comprising: a transponder deployment mechanism, the transponder deployment mechanism deploying a plurality of transponders from the AUV at specified locations in order to form the long baseline navigation network.

11. The apparatus of claim 10 wherein the transponder deployment mechanism is in the interior of the AUV.

12. The apparatus of claim 11 wherein the AUV includes an internal storage location for storing the plurality of transponders prior to deployment.

13. The apparatus of claim 10 wherein the transponder deployment mechanism is on the exterior of the AUV.

14. The apparatus of claim 13 wherein the AUV includes an external storage location for storing the plurality of transponders prior to deployment.

15. A method for calibrating a long baseline navigation network using an Autonomous Underwater Vehicle (AUV), the method comprising: receiving a Global Positioning Satellite (GPS) signal when the AUV is in a surfaced position; identifying, within a record stored in the AUV, a recorded position for each of a plurality of transponders forming a deployed long baseline navigation network; sending from the AUV at least one acoustic sonar signal to the vicinity of the recorded position for at least one of the plurality of transponders; receiving at the AUV at least one acoustic sonar signal from the at least one of the plurality of transponders in reply to the sent signal, the at least one received signal including identifying information uniquely identifying the replying transponder; calibrating in the AUV the long baseline navigation network with a long baseline navigation network calibration module, the calibrating identifying a current position for the replying transponder, the identifying based on the received GPS signal and an analysis of the at least one acoustic sonar signal sent to, and received from, the replying transponder, the long baseline navigation network calibration module updating the record of the location of the replying transponder within the long baseline navigation network to reflect its identified current position; and determining subsequently with navigation software a current location of an AUV using the calibrated long baseline navigation network.

16. The method of claim 15 wherein more than one acoustic sonar signal is sent to and received from a replying transponder and the sending and receiving of the acoustic sonar signals occurs from a plurality of locations.

17. The method of claim 15 wherein the GPS signal is received by a first AUV and the sending and receiving of the at least one acoustic sonar signal is sent and received by at least one other AUV in communication with the first AUV.

18. The method of claim 15 wherein an AUV deploys the deployed long baseline navigation network.

19. The method of claim 18 wherein a one or more other AUVs different from the AUV receiving the GPS signal deploy the long baseline navigation network.

20. The method of claim 15 wherein at least one of the plurality of transponders is an intelligent transponder able to provide information in addition to identifying information in response to a sonar signal sent from the AUV.

21. The method of claim 20, further comprising: receiving current depth information for the intelligent transponder; using the current depth information in calibrating the long baseline navigation network.

22. The method of claim 20, further comprising: receiving information relating to the distance of the intelligent transponder from at least one of the plurality of transponders; using the information relating to the distance of the intelligent transponder from at least one of the plurality of transponders in calibrating the long baseline navigation network.

23. The method of claim 20, further comprising: receiving information relating to the distance of the intelligent transponder from each of the plurality of transponders ; using the information relating to the distance of the intelligent transponder from each of the plurality of transponders in calibrating the long baseline navigation network.