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Improved Geocoder Integration For HIPS and SIPS Software
A Pending Update to HIPS and SIPS Resolves a Number of Issues, Creating Mosaics More Similar to Those From Standalone Geocoder

Jörn Hatzky
Product Specialist
Corey Collins
Product Manager
Kar Wing Wong
Senior Software Developer
Fredericton, Canada

Geocoder is a software toolset that processes acoustic backscatter data for mosaic creation and seafloor characterization. It was developed by the University of New Hampshire and released under license in 2006 to a consortium of specialized software companies that work closely with the university's Center for Coastal and Ocean Mapping (CCOM). The software has been the focus of much discussion within the ocean mapping industry as the desire to take advantage of its capabilities has become more pronounced.

CARIS has worked with the CCOM to integrate the Geocoder toolset into its products. The toolset was integrated with CARIS HIPS and SIPS software to ensure that Geocoder's new features worked in conjunction with pre-existing and well understood workflows. A tight integration makes the tools simple for new users to learn and facilitates future extensions. Geocoder was made available for the first time in HIPS and SIPS version 7.0 in August 2009. CARIS also chose to support a variety of sonar formats to maximize flexibility for the end user.

CARIS has been working to address issues with its Geocoder integration, as well as to address some problems in the standalone Geocoder toolset on which the integrated system is built. The issues relate primarily to differences in the appearance the mosaics produced using HIPS and SIPS and the mosaics produced by the standalone Geocoder. To resolve these issues, CARIS collaborated with the University of New Hampshire on further research and development. These improvements will be released this October in HIPS and SIPS 7.1 Service Pack 1 (7.1.1).

Investigation and Findings
In order to conduct a thorough and fair investigation, CARIS used a baseline data set of backscatter data from a Kongsberg (Kongsberg, Norway) EM 3002 dual-head multibeam sonar. It is important to note that though some of the problems were found to be specific to the processing of data from certain sensors, other problems were independent of the data format or sensor type. RESON (Slangerup, Denmark) multibeam and sonar data logged in Hypack Inc.'s (Middletown, Connecticut) HYPACK software were also tested, but to a lesser degree. Using the EM 3002 data set as a test bed, the evaluation uncovered issues with both the standalone Geocoder and its integration into HIPS and SIPS.

Simrad Data Issues. Two issues with the standalone Geocoder related to the EM 3002 data. Firstly, the standalone Geocoder understood each head of the EM 3002 as having 256 beams rather than the 254 beams that is stated by the manufacturer and used in HIPS and SIPS. This issue could have accounted for some small discrepancies in the HIPS and SIPS software, as different angular offsets can be applied in processing when using a dual-head configuration. For example, the offsets applied would change when crossing over from the last beam on head one (254) to the first beam on head two (255). This was fixed in the standalone Geocoder but is unlikely to be a major contributing factor to the differences seen in the mosaics.

Secondly, unlike HIPS and SIPS, the standalone Geocoder does not use the multiple attitude observations that are stored with the Simrad data. Instead, it simply uses the first attitude observation for the positioning of the samples. The attitude component contributing most to the mosaic differences is heading data, as a small difference in gyro at nadir is exaggerated toward the outer limits of the swath. This could lead to the placement of different intensity values when comparing the outer edges of mosaics from the two systems.

Handling of Data. Issues were also found with the HIPS and SIPS-integrated Geocoder's handling of data from some specific sensors. Geocoder uses opposite sign conventions for pitch and roll than what HIPS and SIPS was expecting, so this required the data to be inverted, which was missed during the initial implementation and has now been fixed in HIPS and SIPS 7.1.1. A problem involving the application of physical offsets relating to the specific EM 3002 dual-head configuration was also discovered and has been fixed.

Encoding of Intensity Values. The most important sensor-independent issue found in the Geocoder integration was the absence of a necessary equation to scale encoded backscatter intensity values back to decibels. To continue this article please click here.

Jörn Hatzky, a product specialist at CARIS, received a diploma in survey engineering from the Technical University of Berlin and a Ph.D. in natural sciences from the University of Bremen. He worked with multibeam backscatter, side scan and sediment echosounder data at the Alfred Wegener Institute for Polar and Marine Research and with satellite remote sensing data at GAF AG.

Corey Collins, product manager for HIPS and SIPS, received a bachelor of science in engineering from the geodesy and geomatics program at the University of New Brunswick. Before joining CARIS, he worked in hydrography and marine geophysical surveying. He is a professional engineer with the Association of Professional Engineers and Geoscientists of New Brunswick, Canada.

Kar Wing Wong received a master of science in computer science from the University of New Brunswick in 1990 as part of the ocean mapping group and started his professional career with CARIS. As a senior software developer, he is involved in all HIPS and SIPS products.

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