Certain data can be filtered so that only the best quality data is imported to HIPS. The filter is applied to port and starboard beam angles. Currently, advanced filtering is only available for EIVA, GeoAcoustics RDF, Klein SDF, and Hypack *.raw and *.hsx formats.
Filtering and thinning methods are executed within a sector angle interval or a horizontal bin size. The sector angle option divides the swath into sectors according to degree angles while the horizontal bin size divides the swath into horizontal sectors based on a specified across-track distance.
Vessel motion and transducer mounting angles are considered when sector angle and horizontal bin locations are determined.
The thinning factor reduces the number of soundings converted on a per swath basis. The thinning factor uses a power of two reduction control (1/2, 1/4, 1/8, etc.) so that one of two, one of four or one of eight soundings can optionally be converted per swath sector.
You have the option not to convert soundings which have been eliminated because of data thinning, although by doing so, a mismatch is created between the converted HIPS data and the original data file. (Since multi-transducer data is tied to the settings in the vessel file, the full dataset is always converted).
Interface
Advanced filtering is done in the Filtering options dialog box.
Option | Description |
Angle filter (Port/Stbd) | 1. Select the check box to apply a range of beam angles. 2. Set range. |
Range Filtering | 1. Select check box to convert soundings within a specified distance (in metres). 2. Set range. |
Amplitude Filtering | Filter soundings according to amplitude value. For each ping (port and starboard pings are handled separately), the min/max amplitude values are obtained, and samples that fall below the selected percentage (0-50%) are rejected. 1. Select the check box and use the up and down arrow buttons to select a percentage value for rejecting soundings. |
Statistical Filtering | Calculates the mean depth and standard deviation within a swath sector or horizontal bin. It then prevents any soundings that fall outside a multiple of the standard deviation from being converted. The mean within the sector is re-computed. Soundings are sorted by their residual from the mean and those closest to the mean are converted. The actual number of soundings converted from within each sector is determined by the thinning factor, if applied. 1. Select the Statistical Filtering check box to apply. |
Threshold | 1. Set a threshold value (in multiples of the standard deviation) by clicking the up and down arrow buttons. The equivalent confidence value as a percentage is updated in the sigma field as the threshold value is changed. |
Sector Angle | 1. Select the Sector Angle interval option and choose a level in degrees (to a maximum of 10ยบ) by clicking the up or down arrow buttons. |
Horizontal Bin Size | An alternate method to setting a sector angle interval. 1. Select the option and set an across-track distance by clicking the up or down arrow buttons. |
Data Thinning | Select the check box to enable the thinning options. |
Thinning Factor | Select a value by clicking the up or down arrow buttons. |
Output thinned data | Select to convert only non-rejected data. |
1. Set options.
2. Click Next to continue the conversion process.