README FILE FOR SPO DATA SETS: ------------------------------ A. Raw Ship Positions and Gyro Headings, Version 3.0 B. Interpolated Ship Position and Velocity Time Series, Version 3.0 ----------------- R.E. Moritz 28 January, 2000 ----------------- [[This readme file is stored at SPO under the name: ship_position_velocity_heading.v3.readme.txt; The datasets are stored at SPO under the filenames: ship_raw_position_heading_tr.v3.txt ship_spline_position_velocity.v3.data.txt]] DATA PROCESSING: ---------------- The logbooks of the "Des Groseilliers, for the period of the SHEBA Field Experiment, were photocopied by the Canadian Coast Guard and provided to the SHEBA Project Office (SPO). The date, time, GPS position and Gyro heading in the log were entered into a computer file at SPO. These raw data were then plotted for inspection, and compared with other data sets, including the SPO observer logbooks, and Miles McPhee's GPS time series for Ocean City. Based on these plots and comparisons, obvious errors of logbook entries and data entry were identified and corrected where possible. Uncorrectable errors were replaced by the missing data flag. The raw data are given at nominal 4-hour time intervals, although there are some longer gaps. The position data were interpolated using a cubic spline [[Matlab function interp1.m]], to estimate the position and velocity components at hourly intervals. The spline passes through the corrected raw positions in a five-day window centered on each hourly interpolation time. The interpolated time series for longitude and latitude are sampled at the midpoint t* of the five day window to produce hourly estimated positions. The fitted position time series is sampled at (t* + 1 hr) and (t* - 1 hr), and the difference between these positions is divided by the time difference to estimate the two-hour average velocity components at each hour. The velocity estimates are scaled to convert from degrees (lat/lon) per day to centimeters per second. The program that generates this file is interp_ship_xyuv_hi.m Because the "Des Groseilliers" drifted with the ice throughout the experiment, the interpolated velocities represent the velocity of the sea ice in the SHEBA experimental site. **********************NOTE********************************* * * * All dates and times are in GMT * * * * All longitudes are positive WESTWARD from Greenwich * * * * Missing data are listed as -999.9 in the file. * * * *********************************************************** FORMATS: -------- A. Raw Ship Positions and Heading Column 1 = yyyy (year) Column 2 = mm (month) Column 3 = dd (day) Column 4 = hh (hour GMT) Column 5 = LY (north latitude in degrees and decimal minutes) Column 6 = LX (west longitude in degrees and decimal minutes) Column 7 = CC (ship's heading in degrees true) ********************************************************************* * NOTE: There is no punctuation and no space between the "degrees" * * and the "minutes" in the position entries. * ********************************************************************* Example: The following line of data 1997 10 2 2000 7515.90 14238.40 230.0 would be interpreted as follows: The date is 2 October, 1997. The time is 2000 GMT. The latitude is 75 deg 15.90 min North. The longitude is 142 deg 38.40 min West. The ship's gyro reading is 230.0 degrees true. B. Interpolated Ship Position and Velocity Column 1 = yy (year) Column 2 = mm (month) Column 3 = dd (day) Column 4 = hh (hour GMT) Column 5 = ttt.tttt (time in GMT days (0000 GMT on 1/1/97 is time = 0.0, calculated directly from yy, mm, dd, hh) Column 6 = xxx.xxxx (west longitude in decimal degrees, spline interpolated to 1 hour spacing) Column 7 = yy.yyyy (north latitude in decimal degrees, spline interpolated to 1 hour spacing) Column 8 = uuuu.uuuu (eastward component of velocity, in cm/s, spline interpolated to 1 hour spacing) Column 9 = vvvv.vvvv (northward component of velocity, in cm/s, spline interpolated to 1 hour spacing) [[Example: The following line of data 97 10 4 8 276.3333 143.1633 75.3550 -17.1284 9.7043 is interpreted as follows. The Date (GMT) is 4 October, 1997. The time is 0800 GMT. The time is 276.3333 days after 0000GMT on 1/1/97. The longitude is 143.1633 degrees West. The latitude is 75.3550 degrees North. The eastward velocity is -17.1284 cm/s. The northward velocity is 9.7043 cm/s.]] DATA USE AND ACKNOWLEDGEMENT ---------------------------- Users of these data are asked to follow the SHEBA Data Protocol (see http://sheba.apl.washington.edu/data/protocol.html) and to include the following acknowledgement: "Position, Velocity and Heading data sets were provided by the SHEBA Project Office."