The CAMEX-4 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 20Hz. Post flight, subsets of these data are created by averaging data over one second intervals, and reporting a 1Hz dataset of a reduced number of parameters. Thus, four datasets are available for every flight which are:

• The primary is the data collected at 20Hz consisting of all measured and calculated parameters.
• Three 1Hz datasets consisting of:
  • Pressure derived altitude and true air speed and position from aircraft INS system
  • Differential GPS derived position (lat/lon) and altitude
  • Static pressure, Static temperature, potential temperature, u,v, and w components of wind speed

Data Format

File naming conventions and examples of data are as follows:

20Hz Dataset

File names appear as MMyymmdd.20H where:

MM indicates the Meteorological Measuring System data

yymmdd is year, month and date

20Hz indicates 20 Hz data

Data is in ASCII, and each file has a header explaining the data included in the dataset. An example of the 20Hz data header can be found here.

The last eight lines are actually data column headers and data. Due to page constraints, data fills two lines. The units and decimal displacement is shown in the header information. For example, the last value of the last column is 20176. This is an AOA delta P (the column header is Adp) and the multiplier from the table above is 0.001 giving and actual value of 20.176 millibars for the angle of attack delta P.

1Hz Measured and Derived Parameters (by Dataset)

There are three types of 1Hz data as mentioned above. They are:

1. Pressure derived altitude and true air speed and position from aircraft INS system
2. Differential GPS derived position (lat/lon) and altitude
3. Static pressure, Static temperature, potential temperature, u,v, and w components of wind speed

File names for each are as follows:

1. FPyymmdd.DC8
2. MGyymmdd.DC8
3. MMyymmdd.DC8

Again, data is in ASCII. The header section of each file gives information about the particular dataset in a manner similar to that shown in the above table.

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/