Introduction

This document gives an overview of the data available in the Geomagnetic Data Library at the Goddard Space Flight Center. It is intended to supplement NASA GSFC Technical Memorandum 104542, ``Geodynamics Branch Data Base for Main Magnetic Field Analysis" [Langel and Baldwin, 1991].

Since the TM's publication in 1991 several changes have been made. The GSFC IBM Mainframe computer referenced in the Langel and Baldwin [1991] document was shut down in June of 1996. The data files and programs can now be accessed on CD-ROM. Any data stored in IBM binary was first converted to IEEE binary. Each CD-ROM includes the FORTRAN programs used to do this conversion as well as a READ.ME file to explain the format and source of the data. Some file names and directory structures on the CD-ROM's reflect the original IBM tape and cartridge naming convention.

The Geomagnetic Data Library includes original raw data, processed data, project data, and resulting magnetic models. The 1991 TM gives additional information about the original and processed datasets. Several of the special project datasets created at GSFC will be discussed later in this document. The magnetic data in the library covers:

Aeromagnetic Surveys

Surface Surveys

Marine Surveys

Observatory Measurements

Repeat Measurements

Satellite Surveys

Magnetic Models

Geomagnetic Indices

This data originated from many organizations and data centers:

British Geological Survey (BGS)

Geological Survey of Canada (CGS)

Copenhagen University, Denmark

Danish Meteorological Institute (DMI)

Goddard Space Flight Center (GSFC)

Johns Hopkin University Applied Physics Lab (APL)

National Aeronautics and Space Administration (NASA)

National Research Council of Canada

Naval Oceanographic Office (NAVO)

Naval Research Lab (NRL)

National Geophysical Data Center (NGDC)

National Space Science Data Center (NSSDC)

United States Geological Survey (USGS)

Two general purpose routines (AVSIG and EQBIN) were utilized to process much of the data. AVSIG was used to reduce data volume and attenuate high frequency noise for datasets with high sample rates and accurate time information. This was accomplished by averaging approximately 220 km segments along the airplane or ship track. EQBIN was used with sparse data sets. This routine assigned data points to equal area bins, eliminated outlying points, and assigned approximate standard error for each data point. For a complete description of these programs, refer to the ``Geodynamics Branch Data Base for Main Magnetic Field Analysis". These and other programs can be found on:

CD: SURVEYMISC1

Files: /programs/

The next chapter will outline the data available from each of the above sources, the third chapter will give a detailed report on the data processing involved in forming some of the special project datasets, the fourth chapter will list the various data formats, the fifth chapter is a list of the CD's available in the Geomagnetic Data Library, and the sixth chapter is a list of references. Data distributions of several datasets can be found in the Appendix (Chapter 7).

To locate a particular dataset, the user should first refer to Chapter 2. This chapter is organized by data type and source. There are several reports and distribution plots in Chapters 3 and 7 that could assist in this selection process. Once the dataset is chosen, note the CD name, the File name, and the Format Code. Next refer to Chapter 4 for an alphabetical listing of all Format Codes needed to read the data. Chapter 5 lists additional files and formats that are available on the selected CD.