[obspy-users] reading a specific byte from a miniseed blockette

Januka Attanayake jattanayake at yahoo.com
Tue Sep 3 04:38:45 CEST 2019


Hi All, We have a custom built Güralp seismic instrument for which we need something called a TTL (an integer) embedded in the first byte after blockette 1000 (see the description below) to build the response file. Can someone suggest a way to read specific bytes in a miniseed file? Thanks very much!

MiniSEED files produced by Scream have the TTL value encoded into the first byte of the padding after blockette 1000 within the MiniSEED packet header. This is not part of the SEED standard: it was implemented after a request from IRIS in 2007. Most miniSEED reading programs will completely ignore the extra information, because it is in bytes that are "unused" according to the standard.

The "Fixed Section of Data Header" for blockette 1000 comprises three parts:
   
   - a Type Identifier (8 bytes)
   - a Data Header (40 bytes)
   - the Blockette header (8 bytes for B1000)
   - the encoded data values.

In the case of Steim-compressed data, part (4) must be aligned to a 64-byte boundary (the SEED manual says "Place the data in a data records starting at byte 64"). There are, therefore, eight bytes of padding between (3) and (4). We encode the TTL value into the first byte of this padding and a digitiser type code into the second byte.
 
Januka Attanayake
Research Fellow | Earthquake Seismology
Homepage: https://sites.google.com/site/janukaattanayake

School of Earth Sciences | McCoy Bldg. 200 
University of Melbourne | Parkville 3010 VIC 
Australia
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