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Appendix 1: File and data structure
File Structure:
GTS file consists of file descriptor, file layout and data record blocks.
1)
File Descriptor Block
GTS file starts with file descriptor block. So the byte number below is referenced from the
beginning of the file.
Byte 0, 1(unsigned integer)
: It is 4645H. This integer identifies the file as GTS file format
described in this document. The first byte is 45H and the second is 46H in a little endian
machine. To make things simple, this document is based on little endian. If someone uses a big
endian machine to read the file, the bit order needs to be reversed for multiple-bytes field.
Byte 2 ,3(unsigned integer)
: Are the bytes of the file descriptor block without the free string
part, it is 205 for version 1.
Byte 4(Unsigned Integer):
Is the version number. It is 1 at time of documenting, May5, 2016;
Byte 5(Unsigned Integer):
Number of Transmitter Dipole. The value is 2 for tensor measurement;
otherwise it will be 1;
Byte 6(Unsigned Integer):
Number of segment. The segment concept comes from 3D seismic
layout. It is normally 1 and a maximum 2 without an LTU in Geode EM3D.
Byte 7(Unsigned Integer):
Number of Boxes in the layout.
Byte 8(Unsigned Integer):
Number of channels in the layout.
Byte 9(Unsigned Integer):
Number of coils in the layout.
Byte 10(Unsigned Integer):
line frequency, either 50 or 60 Hz;
Byte 11(Unsigned Integer):
0 if using GPS time, 1 if using PC time.
Byte 12(Unsigned Integer):
0 if using UTC time, 1 if local time;
Byte 13(Unsigned Integer):
Type of configuration: 0-MT, 1-Scalar CSAMT( Ex & Hy ),
2-2H Scalar CSAMT( Ex, Hx, Hy), 3-Vector CSAMT ( Ex, Ey, Hx, Hy), 4- Tensor CSAMT;
Byte 14(Unsigned Integer):
Current Tx in use for tensor CSAMT, either 1 or 2;
Byte 15(Unsigned Integer):
Tx type, planning for future use, 0- dipole source, 1-horizontal loop ...
Byte 16(Unsigned Integer)
: Filter Mode. It is 1 if tracking local noise peak, 0 if not;
Byte 17,18,19,20(Unsigned Integer)
: The bytes of the file descriptor free string ( explained later);
Byte 21,22,23,24(Unsigned Integer)
: Minutes of CSAMT frequency stepping cycle;
Byte 25,26,27,28(Unsigned Integer)
: Seconds of CSAMT frequency switching;
Byte 29,30,31,32(Unsigned Integer)
: Maximum seconds of a record transfer time (unused).
