Sensor system with time division multiplexing telemetry
First Claim
1. The method of telemetering signals from an array of sensors being n in number which comprises the steps of time division multiplexing said sensor signals by deriving analog samples of said sensor signals successively from different ones of said n sensors, continuously monitoring said signals during successive overlapping to provide said analog samples, and transmitting said samples during successive non-overlapping time slots shorter than the slots of said analog samples.
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Abstract
A seismic array containing a large number of seismic sensors, which may be optical hydrophones, has successive sections, each of which contains a subarray of sensor channels, interconnected by a fiber optic signal transmission line via telemetry modules. Synchronizing signals for initiating successive scans of the sensors in the array and timing the multiplexing of the channels are transmitted along the signal transmission line from the tail end of the line through telemetry modules to the head end. Equipment for receiving, demultiplexing and processing the seismic data is provided at the head end. The array may be towed as a seismic streamer and the head end equipment located topside on the towing vessel. The telemetry modules provide hybrid optical/electrical operation such that array sections including the optical hydrophones and fiber optic links are coupled to each other exclusively by electrical connectors. Submultiplexing of each subarray of sensors (hydrophones) is carried out by the telemetry module under control of scan synchronizing and timing signals so as to avoid the need for anti-aliasing filters and sample and hold circuits associated with the hydrophones in the array, while improving the signal to noise ratio of the seismic data signals derived from the array, in spite of shot or photon noise and also minimizing timing skew errors.
73 Citations
56 Claims
- 1. The method of telemetering signals from an array of sensors being n in number which comprises the steps of time division multiplexing said sensor signals by deriving analog samples of said sensor signals successively from different ones of said n sensors, continuously monitoring said signals during successive overlapping to provide said analog samples, and transmitting said samples during successive non-overlapping time slots shorter than the slots of said analog samples.
- 6. The method of telemetering signals from an array of sensors which comprises the steps of time division multiplexing said signals by sampling said signals to provide analog samples such that the samples from the same sensor are repetitive at a first rate higher than the Nyquist rate for the highest frequency component of interest of said signals, transmitting said samples to a receiving station sequentially at a second rate which is approximately proportional to said first rate multiplied by number of sensors in said array, demultiplexing and filtering said samples at said receiving station to provide output signals, time division multiplexing said output signals at a third rate lower than said first rate which is at least as high as said Nyquist rate for the highest frequency component of interest, and processing said multiplexed output signals to provide data from said array.
- 12. The method of telemetering data from an array of sensors arranged in a plurality of subarrays, each of which subarrays having a plurality of said sensors, which comprises the steps of time division multiplexing said signals into successive groups of successive second samples, each second sample in each group of second samples being from a different one of said subarrays of sensors, by submultiplexing the outputs from each sensor in each subarray into first samples during successive first time slots equal in number to the number of said subarrays in said array, and multiplexing said first samples during successive second time slots shorter than said first time slots and each at the end of a consecutive one of said first time slots to provide said successive groups of second samples where each second sample in each successive group is from a different one of said subarrays of sensors.
- 27. A fiber optic seismic streamer system comprising a plurality of sections each extending from the tail to a head end of said streamer, each section including a fiber optic transmission line having means for translating electrical signals into optical signals at the end thereof toward the tail end and optical signals into electrical signals at the end thereof toward head end, each section also including a subarray of optical hydrophones each having means for producing outputs representing acoustic signals incident thereon when illuminated and providing electrical signal outputs, each section also including a telemetry unit connected to said hydrophones and to a junction of said line, said telemetry unit having means for time division multiplexing said hydrophones by successive illumination thereof and deriving analog samples of said electrical outputs therefrom, means for transmitting successively trains of consecutive first synchronizing signals followed by a group of second synchronizing signals at the tail end of said line and transmitting said synchronizing signals along said optical lines to each of said telemetry units for synchronizing the submultiplexing and transmission of said samples such that samples from different hydrophones in successive ones of said sections are transmitted in successive groups after said first synchronizing signal with each group of samples following each of said second synchronizing signals, and means responsive to the signals leaving the transmission line section at the head end of said line for demultiplexing and processing said analog signal samples.
- 29. Apparatus for demultiplexing a serial PAM train of samples from a plurality of sensors which comprises a plurality of charge transfer devices having a signal input, and a plurality of stages between which charges representing signal samples are transferred, and a plurality of clock inputs for enabling the reception of signal samples at said signal input, for advancing said signal samples through said device, for advancing said samples to the output stage of said device, and for transferring said signal samples to said output, means for applying said sample train to said input, means for sequentially applying clock signals at a first rate to one of said clock inputs of successive ones of said devices, said first rate being at least equal to the rate of said samples in said train, means for applying clock signals to another of said clock inputs of all of said devices at a second rate lower than said first rate to enable said samples to be filtered as they propagate through said devices, means for applying clock signals at a third rate to still another of said clock inputs of all of said devices to derive data decimated samples of said PAM signals, and means for successively applying clock signals at a fourth rate to still another of said clock inputs of successive ones of said devices to derive multiplexed output signal samples from said devices on a common line output connected to the outputs of all of said devices.
- 31. Apparatus for telemetering signals from an array of sensors which comprises means for time division multiplexing said sensors to derive analog samples of said signals successively from different ones of said sensors, means for continuously monitoring said signals in real time during successive overlapping periods of time to provide said analog samples, and means for transmitting said samples during successive non-overlapping time slots shorter than the periods of said analog samples.
- 36. A system for telemetering signals from an array of sensors, which system comprises means for time division multiplexing said signals comprising means for sampling said signals to provide analog samples such that the samples from the same sensor are repetitive at a first rate higher than the Nyquist rate for the highest frequency component of interest of said signals, means for transmitting said samples to a receiving station sequentially at a second rate which is approximately proportional to said first rate multiplied by number of sensors in said array, means for demultiplexing said samples at said receiving station to provide output signals, means for time division multiplexing said output seismic signals at a third rate lower than said first rate which is at least as high as said Nyquist rate for the highest frequency component of interest, and means for processing said multiplexed and output signals to provide data from said array.
- 42. A system for telemetering data from an array of sensors arranged in a plurality of subarrays, each of which subarrays has a plurality of said sensors, which system comprises means for time division multiplexing said signals into successive groups of successive second samples, each second sample in each group of second samples being from a different one of said subarrays of sensors, said multiplexing means comprising means for submultiplexing the outputs from each sensor in each subarray into first samples during successive first time slots equal in number to the number of said subarrays in said array, and means for multiplexing said first samples during successive second time slots shorter than said first time slots and each at the end of a consecutive one of said first time slots to provide said successive groups of second samples where each second sample in each successive group is from a different one of said subarrays of sensors.
Specification