• Document: A White Paper about. MiniSEED for LISS and data compression using Steim1 and Steim2
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Contents Norwegian National Seismic Network Technical Report No. 20 A White Paper about MiniSEED for LISS and data compression using Steim1 and Steim2 version 01.00 Prepared by Mauro Mariotti SARA snc – Perugia – Italy www.sara.pg.it mariotti@infoeq.it Terje Utheim University of Bergen – Bergen – Norway www.geo.uib.no terje.utheim@geo.uib.no Dept. of Earth Science, University of Bergen Allégt.41, N-5007 Bergen, Norway Tel: +47-55-583600 Fax: +47-55-583660 E-mail: seismo@geo.uib.no February 2006 Introduction The Live Internet Seismic Server (LISS) is an internet-based distribution mechanism allowing near-real-time data flow from seismic stations around the world to an essentially unlimited number of clients. The clients can be any software capable to read miniSEED packet using TCP/IP sockets. The LISS is claimed to be full functional on Seiscomp, EarthWorm and Antelope. Considering the importance to have a good interchange standard for seismic data miniSEED appeard to be a good choice considering it is widely known and used in the world. The authors of this document Mauro Mariotti and Terje Utheim experienced many problems in coding mSEED starting from the SEED official manual (Standard for the Exchange of Earthquake Data Reference Manual SEED format Version 2.4 August 2004). This document is prepared with the intent of improve the understanding of the mSEED standard and their popular data compression formats. According to the SEED Reference manual: The Standard for the Exchange of Earthquake Data (SEED) is an international standard format for the exchange of digital seismological data. SEED was designed for use by the earthquake research community, primarily for the exchange between institutions of unprocessed earth motion data. It is a format for digital data measured at one point in space and at equal intervals of time. We hope it will be useful How Binary Data Fields are Described in This Manual for the LISS data distribution (direct extract from the SEED Reference Manual pages 33-34) mechanism where a lot of confusion is present at the moment Throughout this manual, we use some conventions to describe the sizes of fields in the SEED format. of the preparation of this Here are the binary data types used in fixed headers and in data blockettes: document. Field type Number of bits Field description UBYTE 8 Unsigned quantity The essential information about IBYTE 8 Two’s complement signed quantity miniSEED UWORD 16 Unsigned quantity Many internet service are WORD 16 Two’s complement signed quantity widely used to transmit analogue ULONG 32 Unsigned quantity LONG 32 Two’s complement signed quantity information such as radio CHAR * n n*8 n chars, each 8 bits long, valid only ASCII 7 bit (7th bit=0) channels, audio streaming and so FLOAT 32 IEEE Floating point number (single precision) on. Seismic data are slightly different being oriented to lower The IEEE floating point format consists of three stored components: a sign (+ or -), an exponent, and a fraction. In the following description of the storage format these notations will be used: frequency, higher dynamic range and higher time precision. Audio s=sign (bit 31) e=biased exponent (bit 30-23) f=fraction(bit 22-0) streaming (like radios or voice over IP application) can tolerate a The sign is the sign of the fraction. Rather than storing the sign of the exponent a bias is added to the exponent, and the biased exponent is stored. IEEE single precision values occupy one 32 bit word as certain grade of data-loss, this is shown above in 68000 byte order. Bits 0:22 store the 23 bit fraction, bits 23:30 store the 8 bit exponent, not allowed in seismic processing and the high order bit 31 stores the sign bit. The 23 bit fraction combined with the implicit leading bit but the capab

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