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Published November 10, 2020 | Version v1
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FastFix Albatross Data: 4-ms Snapshots of Raw GPS L-1 data from Royal Albatross tracked over 1 month in New Zealand

  • 1. Department of Physics, University of Otago

Description

This dataset consists of snapshots the RAW GPS L-1 baseband data from wildlife tracking tags deployed on Royal Albatross near Dunedin, New Zealand. Ten tags were recovered, and from these tags, 70,733 snapshots were stored. Each snapshot is a file FIXXXXX.BIN that contains a header, followed with interleaved 1-bit I/Q data sampled at 8.184 MHz, mixed down to a frequency of 32000 Hz.

The tags are:
* AF18: 10060 snapshots
* AF29: 4135 snapshots
* AF14: 11054 snapshots
* AF31: 3337 snapshots
* AF13: 10801 snapshots
* AFF6: 1888 snapshots
* AF19: 1701 snapshots
* AFF7: 10865 snapshots
* AF17: 10814 snapshots
* AF15: 6078 snapshots

Raw Shapshot Directory Structure

Each tag data is located in a directory. In this is a file START_DATE.TXT that contains the starting date of the clock in the tag. This is stored in ISO UTC format. Within each tag directory are subdirectories that contain groups of 1000 snapshots.

Snapshot File Structure

The header consists of 6 32-bit binary integers which are (in order)

  • rtc_counter_value: Offset in seconds since the START_DATE.txt
  • sample_count: Number of Samples in this shapshot
  • sample_bytes: Number of bytes in this shapshot
  • sample_ms: Snapshot duration in milliseconds
  • sampling_rate: Sampling Rate
  • checksum: A checksum for validating that data.
  • data.....: the remaining interleaved 1-bit I/Q data.


Acquisition Data

In addition, a GPS satellite acquisition has been performed that retrieves the codephase and doppler shift from each of these files (where one or more satellites are visible). These are stored in a JSON file for each tag in the directory 'acquisition'. The following is an example of an entry that has three visible satellites.

    {
        "codephase": [
            0.9030530071552871,
            0.8163265306122449,
            0.7794026875695107
        ],
        "doppler": [
            1161.2103571268162,
            1060.6060606060637,
            -1829.8852286096371
        ],
        "infile": "/freenas/tag/albatross_data/AFF6/00/FIX00287.BIN",
        "rtc": 172502,
        "sample_ms": 4,
        "sampling_rate": 8183833,
        "sv": [
            3,
            6,
            16
        ],
        "x_max": [
            15.513610551034326,
            9.794986743010222,
            21.07684312237483
        ]
    }

FastFix Position Estimates

Processed animal tracks are available in the file fastfix_position_estimates.json. These are JSON formatted arrays of 2D positions (without altitude, as all positions were essentially at sea-level). These have been processed using the FastFix algorithm [https://doi.org/10.3390/s20226480] to recover estimates of the animals position.

 

Notes

This research was partially funded by the New Zealand Ministry of Business, Innovation and Employment (MBIE; formerly FoRST). Grant Number: UOOX0904

Files

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Additional details

Related works

Cites
Journal article: 10.3390/s20226480 (DOI)

References

  • Molteno, T.C.A. Estimating Position from Millisecond Samples of GPS Signals (the "FastFix" Algorithm). Sensors 2020, 20, 6480.