CAMEX-4 MIPS Field Mill

Table of Contents

Introduction

The University of Alabama in Huntsville (UAH) Mobile Integrated Profiling System (MIPS) includes a 915 MHz Doppler profiler, lidar ceilometer, 12 channel microwave profiling radiometer, Doppler Sodar, Radio Acoustic Sounding System (RASS), Field Mills, and surface observing stations.

This dataset consists of data from the MIPS field mill which yield information about the atmospheric electrical field above the instrument.

The electric field mill is a device used to determine the size of an electric field component. The device consists of two metallic coaxial disks of the same radius separated by a fixed distance. The axis of these disks is pointed in the direction of the field component to be investigated. The lower disk is radially segmented and fixed in position. The upper disk has similarly segmented but has alternate segments removed. This upper disk is rotated and alternatively shields and exposes the fixed disk to the atmospheric electric field. As that disk rotates the electric field flux to the lower segments undergoes continual change that induces a fluctuating voltage between the plates. Knowledge of this voltage and the distance between the disks permits the determination of the electric field component. The instrument is able to detect the rapid change in the electric field which allows for the detection of lightning strikes and electric charges in the area of the electric field mill. Data from the field mill is gathered and recorded in a DOS based program.

A more detailed description of the theory and operation of the electric field mill is found here. Although this link discusses an airborne field mill, the ground based field mill operates in a similar manner.

Data is in a binary data file. Data files are created for each daily (mission) whose name is of the form:

c4gmipfm_2001.228.bin

where c4gmipfm represents CAMEX4 ground station MIP field mill, 2001.ddd is the four digit year and day of year. The .bin extension indicates that these data are in binary form.

The following information comes from the Interface Control Document for Launch Pad Lightning Warning System for the Electric Field Mill, paragraph 6.1 Data Record Structure and begins to describe the binary output file. The entire document is supplied in PDF form with the dataset, or may be found here.

The data record transmitted by the Electric Field Mill consists of 114 bytes of mill operational status, potential gradient, raingauge data, and an error checking parameter. The data record is summarized below with the "Byte No." indicating the number or position in the data record and the "Type" specifying the format of the information:

I = Two's complement 16 bit integer, Motorola byte order
UI = Unsigned 16 bit integer
BI = 16 bit binary pattern
C = Two's complement 8 bit integer
UC = Unsigned 8 bit integer
BC = 8 bit binary bit pattern
X = Not defined
Byte no. Type Function
1-2 BI Synchronization Pattern
3 UC Station Address
4 BC Mode/Command Byte
5-11 - Status Bytes 1-7
12 UC Rain Gauge Tip Count
13-112 I/- Potential Gradient Data or Extended Status Report
113-114 BI CRC-16 Value

Depending on the operating mode of the mill, the data record transmitted will be of one of four types distinguished by the contents of the 100 byte Potential Gradient Data or Extended Status Report:

Contact Information

The data producer is:

Dr. Kevin Knupp
UAH
320 Sparkman Dr.
Huntsville, AL  35805

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/