Rodríguez, I.

Sallarès, Valentí

Simon, Carine

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Instrumentation ViewPoint. Autumn 200560The data ready signal from the A/D converter isused as IRQ7 (event 1 in figure 2). This signalproduces a tree read cycles (24 bits data) andthe data time mark is read. So, the SYSPP driverwas designed to time stamp and data read everytime that an IRQ7 is received. Data are stored ina buffer and later saved on hard disk. The figure3 shows the data acquisit ion process.This prototype of a digital seismic station wasrunning at the ROA for several months with anexcellent results (figure 4 shows an example),and nowadays is being modified including newdata format (mseed).3. Conclusions.A high resolution acquisition system has beendeveloped in the Royal Naval Observatory withan extended response. It is based in a Linuxembedded PC.Data are acquired using the parallel port and itallows save the two serial ports for external andGPS communications.The software PLL time reference rise anaccuracy better than 700 microseconds in theworst case.EPP mode allows a high data transfer rate(>500KB/s) being the data read cycles hardwarecontrolled.A prototype was running at ROA for severalmonths and nowadays is being modified. A newprototype will be available in a few months toupgrade the ROA short period network.4. References [1] A. Pazos, G. Alguacil, and J. M. Davila(2005) A simple technique to extend theBandwidth of electromagnetic sensors, B.S.S.A.Vol 95 Nº 5, pp 1940-1946. [2] A.Pazos, Estación sísmica digital.Tratamiento digital de señales, Boletín ROANº2/2004, San Fernando, 2004. [3] Warp Nine Engineering, IEEE 1284 info, ,2002.Figure 4. Sanlucar earthquake 18/07/200321:23:21, mb=3.7, recorded by 3 stations on thesame pier.A new software tool for Wide-Angle reflection/refraction Seismic dataProcessing And Representation (WASPAR)I. Rodríguez (1), V. Sallarès (2), C. Simon (2)(1) Dpt. Electrical and Electronic Engineering, Public University of NavarraE-31006 Pamplona, Spain.iban.rodriguez@unavarra.es(2) Marine Technology Unit, CSIC, E-08003  Barcelona, Spain.1. Introduction.The seismic methods are the most powerfulexisting techniques to image the structure of theEarth’s subsurface at different scales. Dependingon the system layout, the seismic methods canbe divided in: near-vertical reflection (NVS)techniques and wide-angle reflection/refraction(WAS) techniques. In contrast to NVS, where awide number of tools have been designed by oilindustry, the development of WAS pre-processingtools has deserve only minor attention to date.Most existing tools have been developed byresearch institutions in order to read raw datafrom their own instruments, construct and displaythe record sections, and pick the seismic phases.WAS processing is also done using existing toolsas Seismic Unix [1], but these tools have beenchiefly designed for NVS geometries and not allthe techniques are therefore well-suited for properWAS processing.With all this information at hand, the main purposeof this work has been to develop a new tool forWAS data representation and signal processing.We have thus created the multi-platform modularsoftware tool WASPAR that allows a user torepresent and process data from its initial state(raw data) to its final state (processed recordsection) using a unique and friendly interface.WASPAR has been designed using a plug-inarchitecture to manage all processing modulesand raw data access. In that way, it is easierto maintain the software tool as well as toexpand it with new functionalities. We havechosen C++ programming language to facilitatethe development of a multi-platform softwaretool, which is already available on Linux andMS Windows.2. Program descriptionThe tool we have developed is an open andfree multi-platform software. It has beendesigned as a generic tool, originally developedto process active wide-angle reflection/refractiondata using a unique interface. The mainInstrumentation ViewPoint.Autumn 200561implemented functionalities in this first releaseare those necessary to process wide-angle data.Firstly, the program can potentially read rawdata recorded by any supported equipment. Wehave implemented a plug-in architecture tosimplify the process of adding any new raw dataformat.  Hence, when adding a new format, onejust has to define a new library (or plug-in) whichthe program will be able to interpret. WASPARcan then use this raw data to create a timerepresentation or a record section.Secondly, the program is capable of performingtwo different types of representation: recordsections or time series. In the first one the datacreated in the generation process or the dataread from a seismic file in SEG-Y or SU (SeismicUnix) format are displayed into traveltime-offsetdiagrams (Figure 1). The representation is thenmade taking into account some parameterssuch as fixed-gain, distance-gain, threshold andspeed reduction. All of them are auto-adjustedby the program but the user can check andmodify them by hand. It is also possible toperform phase-picking operations over the recordsection representation. In time representationmode, the program uses a single trace from therecord section or a raw data trace. In bothrepresentation modes, the user is able to performvarious types of zoom and to send therepresentation to the printer or to an image filethat handles different formats.Finally, the program includes a number ofprocessing facilities and, thanks to its plug-insarchitecture, allows easily implementing newones. Each processing technique is includedinto a different library that is recognised by theprogram. The first release includes twoprocessing techniques consisting in a simplefrequency filter and a more elaborated onebased on polarization properties [2].3. Program designWe have designed the program to be modularin order to simplify its development andmaintenance but specially its expansion. Forthat reason, all the functionalities describedabove have been encapsulated into modulestrying to make them as transparent as possible.As shown in figure 2, the program has threemain modules: the program base (M-I), therecord section generation (M-II) and the plug-in module (M-III).The program base has been sub-divided in threemodules (as depicted in figure 2). M-I performsthe main functions of the program and controlsthe execution of the other two modules. It controlsall the file access operations such as loading,saving and format conversion. It also performsall the representation operations such as zoom,phase-picking, control of parameters and imageoutput to printer or file.The record section generation module performsthe fusion of navigation data with station databased on some parameters given by the user. With a wizard-like interface, the moduleincorporates all the necessary information tocorrect station clock drifts and perform the fusion.The result of this fusion is a record section thatcan be saved to a file.The plug-in architecture makes the programscalable and easily expandable: usually, whena new functionality has to be added to a softwarepackage, the source code must be modified andre-compiled. With this architecture, when a newfunctionality is needed, it only has to be createda new plug-in without changing the programsource code. We have used this architecture tomanage all the processing techniques and thedifferent raw data formats.4. Future workThere are still some functionalities to be addedto this software package. The most importantone is an algorithm to relocate receivers inmarine experiments using OBS (Ocean BottomSeismometers), where the position of theinstrument is not exactly known.Apart from this, we are developing new signalprocessing techniques suitable for wide-angleseismology that will be added to the program inFigure 1. Main program  window.Figure 2. Program Flux DiagramInstrumentation ViewPoint. Autumn 200562the future. We are now working on phase-weightedstack algorithms [3], in order to adapt them to theprocessing sequences of wide-angle seismics.5. AcknowledgementThis work was supported by the projectSigSensual ref. REN2003-08341-C03-C01-02and CTM2004-04510-C03-02, the MarineTechnology Unit, the Public University of Navarraand the Catalan Polytechnical University, SPAIN.I. Rodriguez and C. Simon are financed by I3Pcontracts.6. References[1] Seismic Unix, Center for Wave Phenomena,C o l o r a d o  S c h o o l  o f  M i n e s ,ht tp : / /www.cwp.mines.edu/cwpcodes/[2] S. Ventosa, C. Simon, M. Schimmel, Signalprocessing techniques applied to seismic signaldetection, Martech, 2005.[3] M. Schimmel, H. Paulssen, Noise reductionand detection of weak, coherent signals throughphase-weighted stacks, Geophysical JournalInternational,  1997.Signal processing techniques applied to seismic signal detectionS. Ventosa (1), C. Simon (1), M. Schimmel (2)(1) Unitat de Tecnologia Marina,Pg. Marítim de la Barceloneta 37-4908003 - Barcelona - SpainEmail: sventosa@utm.csic.es.(2) Instituto de Ciencias de la Tierra ‘Jaume Almera’08028 - Barcelona - Spain1. IntroductionWide-angle reflection/refraction seismics (WAS)is one of the most commonly used techniques todetermine the structure of the Earth’s crust. Theacquisition system includes a number of energysources and receivers located at increasingdistances from the sources that record both thereflections and the continuous refractions of theseismic waves propagating into the medium. Dataare represented in the so-called record sections,which display recordings of the different sourcesregistered by a given receiver (or vice-versa) intooffset-travel time diagrams.Useful seismic phases present in the recordsections are usually masked by different types ofnoise, which may be caused by the instrument(electronic noise, quantification …), by theenvironment (ship noise, cetacean, sea wavecourse, currents …), or even by the signal itself(higher order reverberations and scattered signalswhich obscure later arriving prominent phases).In order to obtain as much of the valuableinformation contained in the record sections aspossible, it is necessary to process the collecteddata in order to either (1) improve the signal tonoise ratio, or (2) remove or attenuate some wellcharacterized phases, such as the water waveor the first reverberations.Most of existing techniques to improve the signalto noise ratio assume that noise is stationary andGaussian. However, this is usually not the case,so it is necessary to apply alternative techniquesfor an improved signal detection.  These methodsare usually based on nonlinear signal processingtechniques that make use of other signal propertiesthat are more robust against outliers, such asmedian estimators.2. Polarization filtersOne of the techniques used in order to distinguishsignal form noise are filters based on the degreeof polarization [1-2]. [1] and [2] define a signalby an arbitrary but constant polarizationthroughout the course of the signal. This meansthat these filters use the complete wavefield,i.e., the three components of the geophone, tomeasure the variation of polarization alongtraces regardless its category (lineal, circularor elliptic) or direction.According to the characteristics of the signal toprocess, we have considered two relatedtechniques: one works in the time domain,whereas the other one works in the time-frequency domain through a windowed FourierTransform (e.g., Short Time Fourier Transform,S-Transform).  Alternative approaches, suchas the Wavelet Transform can be employed.Figure 1: Three-component test data and itsdegree of polarization.  The polarized signal isindicated by the grey background.

A new software tool for Wide-Angle reflection/refraction Seismic data : Processing And Representation (WASPAR)

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