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Documentation of the U.S. Geological Survey Oceanographic Time-Series Measurement Database

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Content Overview

Although each type of sensor or instrument collects and stores data in a proprietary format, all the information provided in this database has the same format. A common methodology is used to treat all the kinds of data collected, and create files of a format called the Network Common Data Format (netCDF). All the processing steps, are discussed in the Data Processing section, and more detailed information about NetCDF is provided in the NetCDF storage section. The following paragraphs provide an overview of what the user can expect to find in files in this database. The files in this database each contain data from one instrument, and since current meters don't typically also measure hydrographic properties, a user must access several files to examine both velocity and temperature data.

Five coordinate variables define the dimensions of the data in all our data files. The depth of the measurement, latitude and longitude specify the location of the observation in space. Time is the fourth variable, but because of historical accuracy issues related to the number of bits older computers could access, the time of the observation is encoded as two variables. The first time variable ("time") is true Julian Day (May 23, 1968 = 2440000); the second time word ("time2")is milliseconds (msec) from 00:00 on that day. The actual time in days may be computed as time + (time2/86400*1000) [the conversion uses 86400 seconds per day and 1000 milliseconds per second].

Table 1 lists the variable name and the matching long name and units for variables typically found in the database. Each file will contain a subset of the variables based on the kind of data the instrument collected. Some variables have alternate older names which are also listed.

Table 1: Variable names common in the time-series database.

Coordinate variables

Variable nameContents (units)
Time Time (true Julian day)
Time2 Time (msec since 00:00 GMT)
Depth Depth (m) (may be scalar or vector)
Lat Latitude (decimal degrees)
Lon Longitude (decimal degrees)

Currents

Variable nameAlternate nameContents (units)
u_1205 East eastward velocity (cm/s)
v_1206 North northward velocity (cm/s)
w_1204  vertical velocity (cm/s)
CD_300vdir_1 current direction (degrees)
CS_310 vspd_1current speed (cm/s)
Werr_1201  error velocity (cm/s)
AGC_1202  average echo intensity (percent)
PGd_1203  percent good pings (percent)
hght_18   height of sea surface (m)

Hydrographic Properties

Variable name Alternate name Contents (units)
P_1 pressurepressure (db)
P_4 pressurepressure (Pascals)
P_4023 average burst pressure (mbar)
T_28temperaturetemperature (°C) (ITS-1990 standard)
Tx_1211 ADCP transducer temperature (°C)
C_51conductivityconductivity (S/m)
S_40salinitysalinity (PPT)
S_41salinitysalinity (PSU)
STH_71sigma_theta density (kg/m³)

Turbidity

Variable name Alternate name Contents (units)
tran_4010  transmission (volts)
ATTN1_55  Beam attenuation (m-1)
NEP1_56  backscatter intensity (volts)
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This page last modified on Monday, 24-Nov-2014 12:28:49 EST