The CAMEX-3 DC-8 Meteorological Measurement System
Table of Contents
 Introduction
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.
System Description
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.
Data Reported to MMS
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.
Primary Products (1Hz & 5Hz) Typical value at 40,000 ft:
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)
Secondary Products: (1Hz & 5Hz)
Measured
positions
velocities
accelerations
pitch
roll
heading
angle of attack
angle of sideslip
dynamic & total pressures
total temperature
Calculated
potential temperature
true-air-speed
turbulence (0.8 - 1.5 Hz)
Data Format
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.
5Hz Data
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
BUI, T. P.; S. Bowen; C. Chang; J. Dean-Day; L. Pfister; A. Trias
NASA - Ames Research Center
Meteorological Data from DC-8 MMS
CAMEX-3
1 1
1998 08 03 1999 11 02 ;flight-date process-date
0
Elapsed UT seconds of flight date
24
.1 .01 .01 .01 .01 .001 .01 .001 .001 .1 .01 .01
.01 .01 .01 .01 .001 .01 .01 .01 .0001 .001 .001 .001
99999 99999 99999 999999 999999 999999 99999 999999 9999999 999999 99999 99999
99999 99999 999999 999999 999999 999999 99999 99999 999999 999999 999999 999999
Static Pressure (Psta) mb 0.1 99999
Static Temperature * (Tsta) K 0.01 99999
True Air Speed * (TAS) m/s 0.01 99999
E-W Horizontal Wind Speed * (U) m/s 0.01 999999
N-S Horizontal Wind Speed * (V) m/s 0.01 999999
Vertical Wind Speed *@ (W) m/s 0.001 999999
Log10 Turbulent Dissipation * (TEDR) kW/kg 0.01 99999
Latitude +N (LAT) deg 0.001 999999
Longitude +E (LONG) deg 0.001 9999999
Hydrostatic Altitude (HALT) m 0.1 999999
Potential Temperature * (POT) K 0.01 99999
Roll Angle +right wing down (ROLL) deg 0.01 99999
Heading Angle (HDG) deg 0.01 99999
Pitch Angle (PITCH) deg 0.01 99999
N-S Ground Speed +N (Ydot) m/s 0.01 999999
E-W Ground Speed +E (Xdot) m/s 0.01 999999
Vertical Speed +U @ (Zdot) m/s 0.001 999999
Q (Compressible Dynamic Pressure) (q) mb 0.01 999999
Yaw Angle (sideslip angle) (YAW) deg 0.01 99999
Angle of Attack (AOA) deg 0.01 99999
Mach Number (MACH) 0.0001 999999
Vertical Acceleration +U (Zdotdot) m/ss 0.001 999999
Yaw delta P (Ydp) mb 0.001 999999
AOA delta P (Adp) mb 0.001 999999
3
EGI navigation data
Hydrostatic Altitude is an estimate of geometric altitude, accurate to 50 m.
FINAL DATA
13
@ Supressed when data gap is greater than 10 seconds.
Log10 turbulence values (normally < 0) are sign-reversed when the turbulent
sampling wavenumber is less than the buoyancy wavenumber. Under such
conditions, computed dissipation rates may not be quantitative. See explanation
in Chan et al., "Turbulence Measurements by the DC-8 Meteorological Measurement
System", Geophys. Res. Letters, 25-9, 1355-1358, 1998.
FORMAT(F8.1,3I6,3I7,I6,I7,I8,I7,2I6,/,1x,2I6,4I7,2I6,4I7) (87 & 81-byte per line)
At the request of users in the meteorological community, more significant
\camex.cv\d_980803.cv
GMTS Psta Tsta TAS U V W TURB LAT LONG HALT POT ROLL
HDG PIT Ydot Xdot Zdot Q YAW AOA MACH Zdotdot Ydp Adp
66362.1 9380 30677 8008 -455 -492 309 -619 34906 -117882 6458 31243 -96
23891 642 -4632 -7309 -36 3460 -14 666 2281 442 -4878 15819
66362.3 9380 30679 8024 -459 -507 207 -653 34906 -117882 6460 31245 -87
23899 659 -4645 -7333 54 3474 -13 670 2285 530 -4849 16109
66362.5 9380 30683 8057 -442 -514 465 -693 34906 -117883 6461 31249 -79
23909 676 -4657 -7352 179 3502 -13 697 2294 731 -4849 17582
66362.7 9380 30681 8111 -409 -509 828 -668 34906 -117883 6463 31248 -68
23917 691 -4670 -7371 336 3550 -11 726 2310 797 -4847 19201
66362.9 9380 30680 8181 -367 -495 822 -922 34906 -117883 6465 31246 -57
23926 703 -4681 -7396 510 3613 -10 725 2330 980 -4780 19175
66363.1 9379 30685 8254 -317 -473 874 -783 34906 -117883 6468 31252 -44
23933 714 -4688 -7414 708 3678 -9 725 2351 918 -4781 19186 |
1Hz Data
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
BUI, T. P.; S. Bowen; C. Chang; J. Dean-Day; L. Pfister; A. Trias
NASA - Ames Research Center
Meteorological Data from DC-8 MMS
CAMEX-3
1 1 ;ivol nvol
1998 08 03 1999 11 02 ;flight-date process-date
0 ;0=non-uniform time increment
Elapsed UT seconds of flight date
11 ;number of primary variables
0.1 0.1 0.1 0.1 0.1 0.1 0.01 1.0 0.001 0.001 1.0 ;scale factors
99999 9999 9999 9999 9999 9999 99999 99999 999999 9999999 99999 ;missing values
Static Pressure (mb)
Static Temperature (K)
Theta - potential temperature (K)
U - horizontal E-W wind speed (m/s)
V - horizontal N-S wind speed (m/s)
W - vertical wind speed (m/s)
TEDR - LOG10 of Turbulent energy dissipation rate (kW/kg) (see note below)
Hydrostatic Altitude (m)
Latitude +N (deg)
Longitude +E (deg)
Differental GPS Altitude (m)
4
EGI navigation data
Hydrostatic altitude is an estimate of geometric altitude, accurate to 50 m.
Differential GPS altitude is available only when DGPS signals were received.
FINAL DATA
13
Log10 turbulence values (normally < 0) are sign-reversed when the turbulent
sampling wavenumber is less than the buoyancy wavenumber. Under such
conditions, computed dissipation rates may not be quantitative. For
explanation, see Chan et al., "Turbulence Measurements by the DC-8
Meteorological Measurement System", Geophys. Res. Letters, SUCCESS special
section, 1998.
1Hz data are desampled from 5Hz data.
5Hz data file is available upon request, containing: GMTS,Psta,Tsta,TAS,
U,V,W,TURB,LAT,LONG,PALT,POT,ROLL,HDG,PIT,Ydot,Xdot,Zdot,Q,YAW,AOA,MACH,
Zdotdot,YAWdp,AOAdp. (approx. 3 Mbyte per flight hour)
\camex.cv\d_980803.cv
GMTsec Psta Tsta Thta U V W TEDR H_ALT LAT LONG DGPS_ALT
66364.9 9371 3068 3126 -16 -40 2 -737 655 34905 -117885 99999
66365.9 9365 3067 3125 -17 -39 10 -770 660 34905 -117885 99999
66366.9 9361 3066 3125 -14 -35 1 -807 664 34904 -117886 99999
66367.9 9353 3066 3125 -22 -36 6 -850 672 34904 -117887 99999
66368.9 9347 3065 3125 -14 -36 6 -799 678 34904 -117888 99999
66369.9 9341 3065 3125 -12 -34 3 -857 684 34903 -117889 99999
66370.9 9333 3064 3125 -12 -34 0 -762 691 34903 -117890 99999 |
References
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.
Contact Information
To order these data or for further information, please contact:
Global Hydrology Resource Center
User Services
320 Sparkman Drive
Huntsville, AL 35805
Phone: 256-961-7932
E-mail: support-ghrc@earthdata.nasa.gov
Web: http://ghrc.nsstc.nasa.gov/
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