02 July 2026
Discover how to configure and calculate Total Propagated Uncertainty (TPU) in CARIS HIPS and SIPS. Learn how sensor accuracies and device model parameters influence uncertainty calculations.
Within CARIS HIPS and SIPS, it is possible to compute Total Propagated Uncertainty for varying survey setups for use with TPU analysis tools and within the incorporated CUBE functionality.
The computation of TPU is based on the user's setup of the HIPS Vessel File and corresponding settings in the Georeference Bathymetry process, with estimates of the uncertainty of each individual sensor. In both instances each sensor uncertainty value must be entered as 1-sigma.
Sensor accuracy values can typically be found by searching the manufacturers spec sheets.
To represent the uncertainty in the Sonar range and angle measurements, you can either use the real-time value as recorded by the sonar, or a device model may be selected in the vessel setup. Each device model entry has a number of different parameters which factor into various computations within HIPS and SIPS, including the uncertainty computations. The table below outlines the various entries.
| Entry in Device Models | Description | Units |
| Sonar Specifics | ---- | ---- |
| Max_Num_Beams value | Maximum number of beams on the device | # |
| Operating_Frequency_1 value | Operating frequency 1 (or prime freq.) | kHz |
| Operating_Frequency_2 value | Operating frequency 2 (or zero if 1 frequency) | kHz |
| Max_Angle value | Maximum angle away from nadir | Deg |
| Beam_Width_Across value | Across track beam width | Deg |
| Beam_Width_Along value | Along track beam width | Deg |
| Steering_Angle value | Angle beyond which beams are steered | Deg |
| Range_Sampling_Frequency value | Range sampling frequency | Hz |
| Range_Sampling_Distance value | Range sampling distance | m |
| Min_Pulse_Length value | Minimum pulse length | ms |
| Rates | ---- | ---- |
| Repitition value | Maximum repitition rate | pings per sec |
| Bathy value | Rate of bathymetry packets | packets per sec |
| Attitude value | Rate of attitude packets | packets per sec |
| Imagery value | Rate of imagery packets | packets per sec |
| Density | ---- | ---- |
| Bathy value | Number of packets of bathy information | packets in datagram |
| Attitude value | Number of packets of attitude information | packets in datagram |
| Imagery value | Number of packets of imagery | packets in datagram |
| Device Properties | ---- | ---- |
| Imagery value | Device is a multi-beam (No = single-beam) | Yes / No |
| SideScan value | Device is a true side-scan sonar | Yes / No |
| Towed value | Device is towed/tethered or is being towed | Yes / No |
| Calibrated value | Device backscatter is calibrated in dB | Yes / No |
| DualFrequency value | Device uses two operating frequencies | Yes / No |
| HasAccuracy value | Accuracy information available through device module calls | Yes / No |
| Steered value | Device has steered beams | Yes / No |
| Splithead value | Device has a dual transducer configuration | Yes / No |
| Bathymetric value | Device can generate bathymetry information | Yes / No |
| Imagery value | Device can generate imagery (backscatter) | Yes / No |
| Attitude value | Device can generate attitude datastream | Yes / No |
It is advised that all fields are populated as other fields may become used in future releases of HIPS. Values in bold are required by the HIPS devicemodels.xml
The uncertainty values used within the HIPS Vessel File need to be entered as 1-sigma.
Throughout manufacturer spec sheets there is reference made of uncertainty in several different forms such as 95%, CEP and RMS. HIPS and SIPS requires the 1-sigma value to be entered. Below are some of the relationships between the 1-sigma value and some of the common values found in manufacturer's specifications.
Standard Deviation/Uncertainty is denoted by: σ
Other values which the user may discover when trying to determine the standard deviation:
RMS: Root Mean Square
RMS is often equivalent to standard deviation, when the mean error is zero. In most practical applications, this is the case and RMS can be treated as 1-sigma uncertainty
CEP: Circular Error Probable
This is the radius of a circle that contains a defined percentage of the observations. Often expressed as CEP (50%), or as 95% and 99% circular error radii (R95, R99). For the case where uncertainty is equal in both x and y (σx = σy), the following relationships apply:
CEP 50 = ~1.177 × σ
R95 = ~2.447 × σ
R99 = ~3.03 × σ
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