Introduction
System Description
Data Reported to MMS
Primary Products
Secondary Products
Measured
Calculated
Data Format
5Hz Data
1Hz Data
References
Contact Information
The CAMEX-3 DC-8 Meteorological Measurement System
Introduction
System Description
Data Reported to MMS
Primary Products
Secondary Products
Measured
Calculated
Data Format
5Hz Data
1Hz Data
References
Contact Information
The NASA DC-8 Meteorological Measurement System consists of three major systems: an air-motion sensing system to measure air velocity with respect to the aircraft, an aircraft-motion sensing system to measure the aircraft velocity with respect to the earth, and a data acquisition system to sample, process, and record the measured quantities
The air-motion system consists of two airflow-angle probes, three total temperature probes each with a different response time, a pitot-static pressure probe, and a dedicated static pressure system. All probes and sensors are judiciously located at specific positions of the fuselage. The aircraft-motion sensing system consists of an embedded GPS ring laser inertial navigation system (Litton LN-100G), and a multiple-antenna GPS attitude reference system (Trimble TANS Vector). The data system rack is located near station 840, and customized software was developed to control, sample, and process all sensors and hardware.
The primary dataset collecting all parameter types (listed in the data format section below), is gathered at 5Hz. Post flight, a subset of these data are created by averaging data over one second intervals, and reporting a 1Hz dataset of a reduced number of parameters. Thus, two datasets are available for every flight and are called 1Hz and 5Hz data. Primary and secondary products used by MMS are listed below.
Pressure =~ 200 mb +/- 0.3 mb or =~ 0.5% br>
Temperature =~ 220 K +/- 0.3 K or =~ 0.2%
Horizontal Wind =~ 30 m s-1 +/- 1 m s-1 or =~ 4.0%
Vertical Wind < 1 ms-1 (Resolution: 0.1 m s-1)
Measured
positions
velocities
accelerations
pitch
roll
heading
angle of attack
angle of sideslip
dynamic & total pressures
total temperatureCalculated
potential temperature
true-air-speed
turbulence (0.8 - 1.5 Hz)
The file name is of the form[Mm0803-5Hz], which tells the date of the flight (yy.ddd) and the type of data (1 or 5Hz). Each of the data files contain a header which describes the data which follows, and an example of the header portion of each type of data file is shown below. The examples below are from the files [Mm0803-5Hz] and [Mm0803-1Hz] respectively.
As seen in the table shown below, most of the entries in the header section of the file are self explanatory, but several are of note:
Line #1 (56 1001) indicates that there are 56 lines in the header (line 57 is the first line of data).
The first reported parameter is GMT in seconds and tenths: e.g. (from the first data line in purple) GMT is 66362.1 which converts to 18:26:02 GMT.
Line #11 & 12 (in blue) indicates the scaling factors for each of the reported parameters beginning with the second parameter. In this case, the scaling factor is 0.1.
Lines #13 and 14 (in green) gives the number of digits reported for each parameter in each data cycle.
Thus, when the first scaling factor from line #11 (.1) is applied to the first number (99999) in line #13, you can determine that the second data parameter is going to have five digits, and will be in tenths. Thus, 9380 reported in the first data line represents 938.0.
Units for the data parameters (again, beginning with the second because the first is GMT seconds) are listed next, and we find that the units of the second data parameter are millibars of static pressure, in the previous example: 938.0 mb.
A format line is provided six lines above the data lines for use with automated output.
|
56 1001
FORMAT(F8.1,3I6,3I7,I6,I7,I8,I7,2I6,/,1x,2I6,4I7,2I6,4I7)
(87 & 81-byte per line)
GMTS Psta Tsta TAS
U V W
TURB LAT LONG HALT
POT ROLL |
Line #1 (42 1001) indicates that there are 42 lines in the header (line 43 is the first line of data).
The first reported parameter is GMT in seconds and tenths: e.g. (from the first data line in purple) GMT is 66364.9 which converts to 18:26:05 GMT.
Line #11(in blue) indicates the scaling factors for each of the reported parameters beginning with the second parameter. In this case, the scaling factor is 0.1.
Line #12 (in green) gives the number of digits reported for each parameter in each data cycle.
Thus, when the first scaling factor from line #11 (.1) is applied to the first number (99999) in line #13, you can determine that the second data parameter is going to have five digits, and will be in tenths. Thus, 9371 reported in the first data line represents 937.1.
Units for the data parameters (again, beginning with the second because the first is GMT seconds) are listed next, and we find that the units of the second data parameter are millibars of static pressure, in the previous example: 937.1 mb.
|
42 1001
1Hz
data are desampled from 5Hz data. |
Chan, K. R., S. W. Bowen, and J. D. Day, Observation of Turbulence by DC-8 MMS, presented at the AEAP Virginia Beach Meeting, VA, April 1997.
Bui, T. P., DC-8 Meteorological Measurement System, presented at the SONEX Workshop, NASA Ames Research Center, February 1997.
Data can be ordered and questions addressed at http://ghrc.nsstc.nasa.gov/.
To order this data or for further information, please contact: Global Hydrology Resource Center
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