NAMMA DC-8 Meteorological Measurement System

Table of Contents

Introduction

The NASA DC-8 Meteorological Measurement System (MMS) is a proven instrument to measure accurate, high resolution, science quality, in situ airborne state measurements. The parameters measured are pressure, temperature, turbulence, and three-dimensional wind vectors. This system was developed at NASA Ames Research Center, has been operational since 1986, and has been successfully used in the following missions: STEP, AAOE, AASE I, AASE II, SPADE, ASHOE/MAESA, SUCCESS, STRAT, SONEX, POLARIS, SOLVE, CAMEX-3/4, CRYSTALFACE, MidCix, AURA Validation Experiment and NAMMA.

These data files were generated during support of the NASA African Monsoon Multidisciplinary Analyses (NAMMA) campaign, a field research investigation sponsored by the Science Mission Directorate of the National Aeronautics and Space Administration (NASA). This mission was based in the Cape Verde Islands, 350 miles off the coast of Senegal in west Africa. Commencing in August 2006, NASA scientists employed surface observation networks and aircraft to characterize the evolution and structure of African Easterly Waves (AEWs) and Mesoscale Convective Systems over continental western Africa, and their associated impacts on regional water and energy budgets. For more information about the NAMMA Campaign, go to the NAMMA web site: http://namma.nsstc.nasa.gov/

The MMS 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, and a multiple-antenna GPS attitude reference system. Customized software was developed to control, sample, and process all sensors and hardware.

Since the MMS provides quality information on atmospheric state variables, MMS data have been extensively used by many investigators to process and interpret the in situ experiments aboard the same aircraft.

The primary dataset, collecting all parameter types, is gathered at 20Hz. A subset of these data are created by averaging data over one or five second intervals, and reporting a 1Hz or 5Hz dataset of a reduced number of parameters. Primary and secondary products used by MMS are listed below.

Primary Products

The primary data are collected at 20Hz consisting of all measured and calculated parameters. The header in each data file explains the data, and list the parameters contained in each column. An example listing is shown in figure 1 below:

FIGURE 1

Secondary Products

Subsets of the primary data are created by averaging data over one or five second intervals, creating a dataset of a reduced number of parameters. These products may include:

Measured Parameters

DGPS Positions, Velocities, Accelerations, Pitch, Roll, Heading, Angle-of-Attack, Angle-of-Sideslip, Dynamic & Total Pressures, Total Temperatures

Derived Parameter

Potential Temperature, True-Air-Speed, Turbulence

GHRC data holdings consist of a 20 Hz primary dataset, named as follows:

NAMMA_MMS_yyyymmdd_mm_20HZ.txt

There are also secondary datasets derived from the primary at 5Hz or 1Hz sample rates. These datasets are named as follows:

NAMMA_MMS_yyyymmdd_xx_dc8.txt

where,

NAMMA_MMS = Campaign and instrument
yyyymmdd = Year, Month, Day
xx = Type of secondary files (listed in "Format and Content" section)
txt = data in ASCII text files

"mm_20HZ" data

This is the primary dataset, and the data are sampled at a 20 Hz rate. This dataset contains all of the MMS parameters which consist of:

Static Pressure (Psta) mb
Static Temperature * (Tsta) K
True Air Speed * (TAS) m/s
E-W Horizontal Wind Speed * (U) m/s
N-S Horizontal Wind Speed * (V) m/s
Vertical Wind Speed *@ (W) m/s
LOG10 Turbulent Dissipation Rate (TEDR) Kw/Kg
LOG10 Reynolds Number per Length (REYN) /m
Latitude +N (LAT) deg
Longitude +E (LONG) deg
Pressure Altitude (PALT) m
Potential Temperature * (POT) K
Roll Angle +right wing down (ROLL) deg
Heading Angle (HDG) deg
Pitch Angle (PITCH) deg
N-S Ground Speed +N (Ydot) m/s
E-W Ground Speed +E (Xdot) m/s
Vertical Speed +U @ (Zdot) m/s 0.001
Q (Compressible Dynamic Pressure) (q) mb
Yaw Angle (sideslip angle) (YAW) deg
Angle of Attack (AOA) deg
Mach Number (MACH)
Vertical Acceleration +U (Zdotdot) m/ss
Yaw delta P (Ydp) mb
AOA delta P (Adp) mb

"ma" data

This reduced parameter secondary dataset is sampled at a 5 Hz rate (from the 20 Hz data), and contains the following parameters:

GMT - Elapsed UT seconds of flight day
Pitch - Pitch angle (deg)
Roll - Roll angle (deg)
Head - Heading angle (deg)

The "fp", "mm" and "mg" reduced parameter secondary datasets are sampled at  a 1 Hz rate (from the 20 Hz data), and contain the following parameters:

"fp" data:

UT - Elapsed UT seconds of flight day
P_ALT - Pressure Altitude (m)
LAT - Latitude (deg)
LONG - Longitude (deg)
TAS - True Air Speed (m/s)

"mm" data:

GMT - Elapsed UT seconds of flight day
Psta - Static pressure (mb)
Tsta - Static temperature (deg K)
Thta - Potential temperature (deg K)
U - Horizontal E-W wind speed (m/s)
V - Horizontal N-S wind speed (m/s)
W - Vertical wind speed (m/s)

"mg" data:

UT - Elapsed UT seconds of flight day
DALT - GPS altitude (km)
DLAT - GPS latitude +N (deg)
DLONG - GPS longitude +E (deg)
TEDR - Log10 of Turbulent eddy dissipation rate (kw/kg)
REYN - Log10 of Reynolds number per unit length (/m)

Each of the dataset files contain a header which describes the data that follows. An example of the header portion of a data file is shown in figure 2 below. 

FIGURE 2

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.

Gaines, S. E., S. W. Bowen, R. S. Hipskind, T.P. Bui, and K. R. Chan, Comparisons of the NASA ER-2 meteorological measurement system with radar tracking and radiosonde data, J. Atmos. Ocean. Tech., 9, 210-225, 1992

S.G. Scott, T.P. Bui, K. R. Chan, and S. W. Bowen, The meteorological measurement system on the NASA ER-2 aircraft, J. Atmos. Ocean. Tech., 7, 525-540, 1990

K. R. Chan, L. Pfister, T.P. Bui, S. W. Bowen, J. Dean-Day, B.L. Gary, D.W. Fahey, K.K. Kelly, C.R. Webster, and R. D. May, A case study of the mountain lee wave event of January 6 1992, Geophys. Res. Letters, 20, 2551-2554, 1993.

T.P. Bui, S. Bowen, C. Chang, J. DeanDay, L. Pfister, R. Castenada, P. Shulman,
Evaluating, WB-57F and ER-2 MMS measurement confidence, CRYSTAL-FACE Science Meeting at Salt Lake City, Feb. 2003

Chan, K. R., J. Dean-Day, S. W. Bowen, and T. P. Bui (1998), Turbulence measurements by the DC-8 meteorological measurement system, Geophys. Res. Lett., 25(9), 1355–1358.

The data provider is:

T. Paul Bui
NASA Ames Research Center
pbui@mail.arc.nasa.gov

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/