Review: Marine Seismic and Side-Scan Sonar Investigations for Seabed Identification with Sonar System

Marine seismic reflection data have been collected for decades and since the mid-to late- 1980s much of this data is positioned relatively accurately. Marine geophysical acquisition of data is a very expensive process with the rates regularly ship through dozens of thousands of euros per day. Acquisition of seismic profiles has the position is determined by a DGPS system and navigation is performed by Hypack and Maxview software that also gives all the offsets for the equipment employed in the survey. Examples of some projects will be described in terms of the project goals and the geophysical equipment selected for each survey and specific geophysical systems according to with the scope of work. For amplitude side scan sonar image, and in the multi-frequency system, color, becoming a significant properties of the sea floor, the effect of which is a bully needs to be fixed. The main confounding effect is due to absorption of water; geometric spread; shape beam sonar function (combined transmit-receive sonar beam intensity as a function of tilt angle obtained in this sonar reference frame); sonar vehicle roll; form and function of the seabed backscatter (proportion incident on the seabed backscattered signal to sonar as a function of the angle of incidence relative to the sea floor); and the slope of the seabed. The different angles of view are generated by the translation of the sonar, because of the discrete steps involved by the sequential pings, the angular sampling of the bottom.

1. Int r oduct i on M arine exploration w ith acoustic system has any function for: m arine seism ic, m arine fisheries, determ ine abundance of fish in m arine fisheries (Lubis and M anik, 2017), Fish stock estim ation echosounder instrument w ith hydroacoustic system (Lubis and W enang, 2016), Echo Processing and Identifying Surface and Bottom Layer . M arine seism ic reflection data have been collected for decades and since the m id-to late-1980s m uch of t his data is positioned relatively accurately. This older data provides a valuable archive, how ever, it is m ainly stored on paper records that do not allow easy integration w ith other datasets. M arine geophysical acquisition of data is a very expensive process w ith the rates regularly ship through dozens of thousands of euros per day. In addition, the survey often rem ote sites and can cause huge overhead on the transit tim e. sub-bottom reflection data has been collect ed for the Decade but m uch older data is stored w ith paperrecords and not so Easy to integrate w ith m odern bathymetric data at this tim e (Ow en et al., 2015).
Seism ic reflection surveys have been used to m ap the sub-surface since 1921 w ith m arine reflection surveys com ing to prom inence in the 1950s w hen they w ere used to m ap bathymetry, seabed identification using m ultibeam and side scan sonar instrument (M anik et al., 2014), seabed identification using side scan sonar C M AX-CM 2 in punggur sea w ith acoustic m ethod .
Sonar system used sound to detect or find objects that are specifically located in the sea. M ultibeam Sonar is an acoustic instrument that has the ability to perform three-dim ensional m apping of the ocean floor (Bartholom a, 2006). The w ater depth m easurem ent using m ultibeam instrument are fast and has a high accuracy, w here this can not be done by a single beam echosounder. In addition to the instrument's ability to perform basic scanningthe seaw at er w ith very high accuracy and coverage are also able to produce inform ation in the form of backscatteringvalues w hich can be used to determ ine the distribution ofseafloor sedim ent type (M anik, 2011).
M odern seism ic data (including m ultichannel seism ics, 3D seism ics and param etric techniques), stored, processed and interpreted digitally, can provide m ore detail than older data (M oham m edyasin et al., 2016). In particular, accurate analysis of reflector polarity (Yoo et al., 2013) m ay not be possible w hen data is converted from a paper record. How ever, this does not m ean that data acquired in t he past is not useful. That acquired since the m id-1980s w ill often have relatively precise and accurate navigation data allow ing integration w ith other m odern datasets w ith acoustic m ethods.
M arine sandy deposits vary in term s of com position, size, thickness, horizontal continuity, and adm ixture w ith other m aterials such as biogenic m atter, m ud, and gravel or rock. According to (de Souza et al., 2015) beach-quality sands have very specific param etric ranges in properties that are acceptable for placem ent on beaches, it is necessary.

Acqui si t i on of sei sm i c profi les
The position is determ ined by an DGPS syst em and navigation is perform ed by Hypack and M axview softw are that also gives all the offsets for the equipm ent em ployed in the survey. Exam ples of som e projects w ill be described in term s of the project goals and the geophysical equipm ent selected for each survey and specific geophysical system s according w ith the scope of w ork. In For am plitude side scan sonar im age, and in the m ulti-frequency syst em , color, becom ing a significant properties of the sea floor, the effect of w hich is a bully needs to be fixed. The m ain confounding effect is due to absorption of w ater; geom etric spread; shape beam sonar function (com bined transm it -receive sonar beam intensity as a function of tilt angle obtained in this sonar reference fram e); sonar vehicle roll; form and function of the seabed backscatter (proportion incident on the seabed backscattered signal to sonar as a function of the angle of incidence relative to the sea floor); and the slope of the seabed. Absorption and geom etrical spreading effect can be corrected relatively straightforw ard. The effect of the functions of the sonar beam and seabed functionality angular backscatter w hich is on the effect of tim e-varied and more difficult to take i nto account. It is only relatively recent ly that sufficient correction has been designed (Tam sett et al., 2016). The seabed backscatters incident sonar signal because: there are acoustic im pedance contrasts across the seabed interface; and the seabed interface is rough in com parison to the w avelength of the sonar carrier w ave.
The seabed interface com prises usually a seabed seabed surfaces bet w een contrasting m aterials. High absorption of ultrasound in sub-seabed m aterials severely lim its the skin depth of the interface. The backscatter response of a seabed to the incident sonar signal, being dependent on seabed interface roughness, is therefore dependent seabed is acoustically colourful (Buscom be, 2017).
That the seabed is intrinsically acoustically colourful m ay be recognised in developing a sonar technology and data at m ultiple sonar frequencies acquired and m apped to optical prim ary colour frequencies to generate optical colour im ages of the seabed for human visualization. The principal advantage of colour im agery over greyscale is that at each pixel, a colour datum occupies a position in a three-dim ensional (3D) RGB (red, green, blue) data space. If colour data are reduced to greyscale, the data in three dim ensions are projected onto and w ill then occupy positions on a line (e.g., the diagonal across the RGB data space). As econdary advantage of colour sonar im ages of the seabed is that they can (subject to the eye of the beholder) be very beautiful (Engquist et al., 2017).

Acoust i c Colour of t he Seabed
Before considering m ethods for rendering m ulti-frequency sonar data as colour im ages,w e look a little m ore deeply at the concept of the acoustic colour of the seabed. W here a sonar syst em is calibrated, the calibrated backscatter am plitude response of the seabed m ay be com puted from : (1) w here: Scal is the calibrated or natural am plitude response of the seabed, this being the ratio of the acoustic signal am plitude backscattered from a seabed to the signal incident on the seabed along the sam e line (0 to 1.0); S is the sonar am plitude response of the seabed (a large integer) corrected for: geom etrical spreading incorporating the effect of the area of absorption, and the sonar beam function (dat a along the trace are norm alised to the response at fram e of reference); Rcal is the ratio of the am plitude response of the sonar receiver in sonar am plitude units (a large integer) to the pressure am plitude at the receiver in micro-Pascal; Tcal is the am plitude of the sonar pulse in m icro-Pascal one m eter from the transm itter in the direction of the reference inclination angle.
The calibrated amplitude response of the seabed Scal, is afunction of sonar carrier w ave frequency ν and angle of incidence w ith respect to the fram e of reference of the seabed (the grazing angle) θ. The function Scal (ν, θ) is tw o-dim ensional and is the broadband seabed backscatter function encapsulating the acoustic backscatter characteristics of a seabed. The dependence on frequency is w hat m akes the seabed acoustically -colour property inherent in Scal (ν, θ) cannot be directly visualised. The generalised function Scal(ν, θ) m ust be reduced to values at three discrete frequencies (or averaged over three frequency bands) and the values scaled to 8-bit values (zero to 255) for display in pixels in digital visual technologies: (2) The values of nDatR (θ), etc., m ay then be used for com puting RGB com ponent s of the natural acoustic colour of the seabed for the frequencies Vlow , Vm ed, Vhigh as a function of grazing angle θ, i.e., the values m ay be used to present the seabed backscatter function m easured by a colour sonar system as a line of colour. To display a sonogram m ontage as a chart, the backscatter values along traces (across sonogram s) are norm alised to the seabed response at the reference inclination angle θref, say 30 (Tam set et al., 2016). At angles m uch less than norm al incidence, the natural backscatter am plitudes are sm all and visually not very distinguishable from shadow . To generate m idrange colours m ore appropriate for practical human visualisation, an am plitude gain m ight need to be applied.
( 3) These values m ay be directly used as param eters for displaying colour for human visualisation or m ay be used as input to a process for generating other RGB param eters for colour display. Optical colour derived from these values should be been generated w ith respect to: the values of the carrier w ave frequencies of the system (or the m eans of bands); the reference inclination angle; and the am plitude gain applied. The relative RGB values are objectively determ ined n data. An exam ple of a colour sonogram presented in RGB colour is show n in Figure 3.
The values for nDatR, nDatG and nDatB are proportional to the sonar amplitudes as a function of frequency. A value of zero represents shadow and appears as black. A value of 255 represent s saturation and appears w hite. A strongly backscattering seabed appears as light shades of colour, e.g., the light shades of blue running up the right side of Figure 3 bare strongly backscattering. Conversely, aw eakly backscat tering seabed appears as dark shades of colour; the dark shades of blue running up the left side of Figure 3 are a very w eakly backscattering seabed. The different angles of view are generated by the translation of the sonar. Because of the discrete steps involved by the sequential pings, the angular sam pling of the bottom w ithin the ranges described in the previous section is not continuous (Haniotis et al., 2015). W e are looking here at the optim al binning of the grazing angles {gi} used to sort the backscatter angular responses, to provide a gapless coverage. The trajectory of the platform is assumed to be a straight line, w ith the forw ard step being a of clarity, one considers the stop and hop scenario. In addition, the angular sam pling is studied in the vertical plane that contains the plat form track, the ground profile being horizontal, at depth h below the antenna.
A point of the bottom lying at the abscissa x ahead of the sonar nadir (y = 0) during a ping is arctan ≪ h, the change betw een successive pings in the angle of view of the sam e 2 g (Fig. 4).
To provide a gapless angular sam pling of the bottom , the longitudinal extent δx of the segm ents intercepted on the bottom by the sectors δγ corresponding to the bin that contains the grazing the sonar bet w een pings, i.e., there m ust be δ An upper bound of the bin w idt hs is given by the few m eters, and the w ater level, h, is a few tens of m eters. Statistics m ade on the processed surveys ‫ץ‬ Given an initial grazing angle γ0 (= 69°), the first part of the partition is thus built recursively by considering constant longitudinal footprints, i.e., ‫ץ‬m ax: For low grazing angles, the w idth of the bins dictated by a constant longitudinal interval δ turns out to be very sm all, w hich is not justified by the experim ental accuracy and increases unnecessarily the number of bins. Consequently, the second part of the partition is built w ith a constant angular bin w idth w hen it reaches a chosen threshold, δ‫ץ‬end = 2° (Fig. 5). The resulting grazing angles at the limit of the bins are displayed in Fig. 6.