SEAS 2000 - XBT File Data Format The Shipboard Environmental (data) Aquisition System (SEAS), is a program developed by National Oceanic and Atmospheric Administration (NOAA) to provide accurate meteorological and oceanographic data in real time from ships at sea through the use of satellite data transmission techniques. The system transmits data through either the GOES or INMARSAT C satellites to NOAA for use in weather, climatological and ocean models. NOAA is actively participating in an international effort to increase the number of subsurface temperature observations in support of global oceanographic and climate studies. NOAA's XBT program (SEAS) currently supports about eighty voluntary observing ships (VOS). For additional information, http://seas.amverseas.noaa.gov/seas/ (last accessed July 28, 2008) The Cyclical Redundancy Check (CRC) is incorporated into the SEAS System. For additional information regarding the CRC, and the data flow, please refer to document seas2_add_info. Field Name Field Description SEAS Version: SEAS Shipboard software version number Ship Name: Ship's Name Call Sign: Ship's Radio Callsign Lloyds Number: Lloyd's Register of Shipping (LR number) A unique seven digit identification number, it remains unchanged for the life of the ship. Date/Time(dd/mm/yyyy): Date of XBT drop (GMT) Latitude(ddd.ddd): Decimal degrees, hemisphere N=north, S=south Longitude(ddd.ddd): Decimal degrees, hemisphere E=east, W=west Ship's Speed: The ship's speed at drop time Probe Type: Type of XBT probe used (4-7,10,11) blank if entry not used. Probe Code: Instrument type for temperature, with fall rate equation coefficients for XBT (WMO Code Table 1770) Probe Serial No: Probe serial number for failure tracking Recorder Type: Type of Recorder used for collecting temperature data Recorder Code: Recorder Code (WMO Code 4770) Bottom Depth: Bottom Depth (meters) GTS CRC: Cyclical Redundancy Check (CRC), Unique Identification of GTS Records. A number derived from, and stored or transmitted with a block of data in order to detect corruption. By recalculating the CRC and comparing it to the value originally transmitted, the receiver can detect some types of transmission errors. SEAS ID: SEAS Identification #. A 32 bit CRC computed on the raw binary SEAS bathy message. INFPTS: Total number of Inflection Points, followed by the data record. (depth,temp) temperature values (to hundredths of a degree celsius) depths (meters to tenths) TWOMETER: Total number of Two Meter Data Points, followed by the data record. (depth,temp) temperature values (to hundredths of a degree celsius) depths (meters to tenths) XBT: Total number of Temperatures Points, followed by the data record. Depths of each sample are not saved because they can be computed by knowing the sample number and probe type. Either Method below can be used to Calculate depths. Method 1: H=A*T-B*T**2 (meters) T = Time step; 0.1,0.2 ....time : time=0.1(# of data points) A and B are the constants determined from the following table: Probe XBT Code Probe WMO1770 Type B A 061 T-10 .00216 6.301 071 T-11 .0002557 1.7779 001 T-4 .00216 6.472 002 T-4 .00225 6.691 011 T-5 .00182 6.828 031 T-6 .00216 6.472 032 T-6 .00225 6.691 041 T-7 .00216 6.472 042 T-7 .00225 6.691 021 T-FD .00182 6.346 051 T-DB .00216 6.472 052 T-DB .00225 6.691 =========================================== Method 2: The depth is calculated from coefficients a and b and the time, t, as follows: z = at + 10-3bt2 or z = a*t + 0.001*b*t*t Probe Probe Coefficient a Coefficient b Code Type 001 Sippican T-4 6.472 -2.16 002 Sippican T-4 6.691 -2.25 011 Sippican T-5 6.828 -1.82 021 Sippican Fast Deep 6.346 -1.82 031 Sippican T-6 6.472 -2.16 032 Sippican T-6 6.691 -2.25 041 Sippican T-7 6.472 -2.16 042 Sippican T-7 6.691 -2.25 051 Sippican Deep Blue 6.472 -2.16 052 Sippican Deep Blue 6.691 -2.25 061 Sippican T-10 6.301 -2.16 071 Sippican T-11 1.7779 -0.2557 201 TSK T-4 6.472 -2.16 202 TSK T-4 6.691 -2.25 211 TSK T-6 6.472 -2.16 212 TSK T-6 6.691 -2.25 221 TSK T-7 6.472 -2.16 222 TSK T-7 6.691 -2.25 THE ACTUAL DATA LOOKS AS FOLLOWS: (1 DROP, PER FILE) SEAS Version: 6.12 Ship Name: Columbus Florida Call Sign: ELZT3 Lloyds Number: 9141132 Date/Time(dd/mm/yyyy): 05/09/2004 23:58 GMT Latitude(ddd.ddd): 025.959 S Longitude(ddd.ddd): 0173.335 W Probe Type: Sippican Deep Blue Probe Code: 52 Probe Serial No: 0000000 Recorder Type: Sippican MK-21 Recorder Code: 6 Bottom Depth: 9999 M GTS CRC: 9079AA94 SEAS ID: 3A842C87 INFPTS: 23 20 2087 750 2040 1090 1993 1870 1883 2530 1718 2850 1630 2990 1596 3250 1530 3720 1365 4090 1272 4300 1197 4590 1120 4820 1061 5170 965 5460 938 5690 848 6100 768 6180 776 7440 658 7870 647 8470 591 8640 578 8840 586 TWOMETER: 442 20 2087 40 2086 60 2084 80 2082 100 2082 120 2079 140 2077 160 2077 180 2075 200 2075 220 2075 240 2075 260 2075 280 2076 300 2076 320 2075 340 2075 360 2076 380 2076 400 2073 420 2073 440 2073 460 2072 480 2071 500 2063 520 2062 540 2062 560 2061 580 2060 600 2060 620 2060 640 2060 660 2060 680 2060 700 2059 720 2054 740 2048 760 2032 780 2026 800 2021 820 2020 840 2020 860 2021 880 2021 900 2021 920 2021 940 2021 960 2020 980 2019 1000 2019 1020 2018 1040 2014 1060 2011 1080 2001 1100 1989 1120 1987 1140 1987 1160 1982 1180 1971 1200 1969 1220 1969 1240 1969 1260 1969 1280 1968 1300 1968 1320 1968 1340 1965 1360 1962 1380 1955 1400 1952 1420 1951 1440 1945 1460 1944 1480 1943 1500 1943 1520 1942 1540 1940 1560 1935 1580 1929 1600 1926 1620 1922 1640 1922 1660 1922 1680 1922 1700 1921 1720 1920 1740 1914 1760 1907 1780 1905 1800 1901 1820 1895 1840 1893 1860 1887 1880 1879 1900 1876 1920 1875 1940 1869 1960 1864 1980 1862 2000 1860 2020 1857 2040 1854 2060 1846 2080 1837 2100 1832 2120 1826 2140 1822 2160 1814 2180 1809 2200 1803 2220 1798 2240 1796 2260 1793 2280 1782 2300 1781 2320 1779 2340 1779 2360 1778 2380 1776 2400 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584 8780 578 8800 576 8820 582 XBT: 1385 21002093208720872086208620862085208520842084208220822082208220822081208020792079 20782077207720772077207720762075207520752073207320752075207520752075207520752075 20762076207720772076207620752075207520752073207320752076207620762077207720762075 20732073207320732073207320732075207320722072207220712070206520632062206220632063 20622062206220612061206120602060206020602060206020602059205920602059206020602060 20602060206020602060205920572056205420532052204820442037203220292028202620252023 20212020202020202020202020202020202120212021202120212021202220222021202120212022 20212021202020202019201820192019202020192018201920192019201820172015201320122011 20102005200219971993198919881987198719871987198719871987198519791976197219701969 19671967196719671968196919691969196919691969196819681968196819681968196819681968 19681967196419631962196219611957195419531952195219511951195119481947194519451945 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644 644 644 644 646 648 648 648 646 646 644 642 640 638 636 634 632 632 632 632 634 634 636 640 642 644 644 646 648 648 648 648 646 644 640 636 632 630 628 628 626 625 625 626 626 626 626 628 630 630 630 630 630 630 628 626 623 619 617 615 615 615 615 613 613 613 613 615 617 617 617 617 615 613 611 609 607 605 603 603 603 603 605 605 605 607 609 609 607 607 605 603 603 601 600 598 596 596 594 594 594 594 594 596 596 598 598 600 600 600 600 598 598 598 596 596 594 590 590 588 588 588 588 588 590 590 592 592 592 590 590 588 584 580 578 576 573 571 569 571 569 567 571 576 578 576 573 573 571 571 575 578 578 578 578 576 575 573 573 573 571 571 571 571 571 576 580 582 584 582 584 584 584 586 584 584 580 578 576 576 576 576 578 582 584 584 The Cyclical Redundancy Check (CRC) is incorporated into the SEAS System. The algorithm used was supplied by MEDS. It is a 32 bit value based on the ASCII generated BATHY message of those values following the 888 group and terminating at the equal (=) sign of the message. Below is a crude description of the SEAS data flow regarding unique record identification. When an XBT is taken, SEAS shipboard software creates a binary record of the entire data stream, metadata, and computed unique SEAS ID for archive aboard ship. This is referred to as the complete message. The complete message is the delayed mode record sent to AOML and forwarded to NODC in the SEAS2K NODC File Format. SEAS shipboard software also creates a best binary message for transmission to Silver Spring which also has the SEAS ID of the archived message on the ship. The SEAS processing servers in Silver Spring essentially build two real time messages from the best message. One is the familiar BATHY (JJVV) formatted record distributed on the GTS to MEDS among other places. (The GTS record reaches MEDS and is incorporated into their GTSPP operation. MEDS computes a CRC and attaches it to the record.) The other real time message is a real time archive message. The real-time archive message contains all metadata and the highest level of bathy information contained in the message transmitted from the ship. For example, if full resolution data were transmitted from the ship, the archive message contains inflection points, two meter data and the full resolution data in SEAS2K NODC format. If only inflection points were transmitted from the ship, the real-time archive file contains only the inflection point data. In either case, the SEAS ID of the original shipboard archive is included as well as the GTS CRC which is computed on the WMO formatted bathy message distributed on the GTS. This archive record is sent to NODC and becomes part of their GTSPP data management operation. Ideally, NODC receives two SEAS records from NOAA. The real-time archive message (SEAS ID + GTS CRC ID) and the delayed mode complete message (SEAS ID). Comparison of the SEAS ID completes the data flow from NOAA. Ideally NODC also receives a GTSPP record from MEDS which has the same GTS CRC ID computed. Comparing GTS CRC ID=s of archive message to MEDS GTSPP record completes the GTSPP data flow. NODC data management determines which record becomes part of the permanent archive.