1. Satellite Derived Bathymetry as Source Data for Navigational Charts

2. Introduction Review of Key findings from UKHO SDB Trial
User group consultation
Charting SDB
Further work
Satellite Derived Bathymetry (SDB) refers to depths processed from optical satellite imagery.
The depth accuracy is where the technology has limitations and this needs to be understood
UKHO have been assessing the accuracy of SDB and the most suitable methodology for representing SDB data on charts.
How can this data be depicted on charts.

3. Satellite Derived Bathymetry?
What Is
Satellite Derived Bathymetry?
Image © DigitalGlobe, 2013
…but dark patches may also be shallow
Shallow=bright
Deep=dark

4. Passive – affected by many uncontrollable factors
Real-world sit
Depth accuracy where technology has its limitations.
uation is complex. More than one method of ‘unmixing’ the spectral signal from which depth can then be derived
Passive – affected by many more uncontrollable environmental factors
Passive – affected by many uncontrollable factors
Spectral ‘unmixing’ is complex, more than one approach

5. Satellite Resolution
Effect of resolution; improved resolution with advancing technology. Object detection.
Good positional accuracy.
Image © DigitalGlobe, 2013
Landsat program
30 metre resolution
WorldView-2 Launch 2009
2 metre resolution

6. Nautical Charts: A Special Case The Cartographic consideration
Use of SDB
Nautical Charts: A Special Case
Purpose of a chart is “to accurately represent nautical information necessary for safe navigation”
ADMIRALTY Nautical Charts comply with International Convention for the Safety of Life at Sea
Data assurance – an essential requirement
Wide application of SDB (Environmental Management, Habitat Mapping & monitoring, Marine Engineering); why charts are different
The Cartographic consideration

7. Antigua: A Case Study
New Chart covering Southern Antigua, scale 1:25,000
New MBES harbour surveys already planned
Existing surveys pre-1852!
Antigua chart requirement already established & New Edition planned

8. Antigua SDB Trial Order 1a Survey carried out Sept-Oct 2013
WorldView-2 image acquired 27 Sept 2013
Tide gauge in place
Horizontal GCPs
Claims of accuracies of 10% of depth were not borne out by early experiences of SDB within the UKHO.
UKHO decided in 2013 to conduct a controlled trial to fully understand the accuracy and reliability of SDB.

9. Antigua SDB Trial
Several different SDB data sets were produced from the same image
Small parts of MBES survey used to calibrate SDB data (ground truth)
Majority of MBES data used as benchmark
Results looked at in terms of:
Overall accuracy (compared to MBES dataset)
Ability to define critical soundings
The imagery was processed using several different SDB processing methods, both in-house and through commercial companies, in order to compare them and understand the repeatability of this technology.
Results were looked at in terms of both overall accuracy (compared to MBES dataset) and SDB’s ability to define critical soundings. These factors were then used to assess a suitable CATZOC classification for SDB data.

10. Results Ground truth applied: Red = SDB datasets Blue = MBES
Brief look at the results (representative of the whole area)

11. Results: Variance ±2m = SDB is deeper = SDB is shoaler ±3m
+/- 3m quoted, but actually +/- 2.75m. Reliability didn’t necessarily relate directly to depth across the area
Survey Standards vs. CATZOC
Difference surfaces were created and coloured to show areas where the SDB data is within 2m and 3m of the MBES data.
The difference surfaces were compared to the depth accuracy requirements for CATZOC C.
±3m

12. Results: Catzoc data passes CatZoc C = data fails
No-ground truth applied: 78% data meets CatZoc C
data passes
CatZoc C
data fails =
more than 97% of the SDB data was within the CATZOC C depth accuracy requirements from the MBES data. Without ground truth data applied only 79% of the SDB data met CATZOC C requirements.
Though more than 97% of the “Commercial Company 1” data could be categorised as CATZOC C, the data that fails CATZOC C requirements is spread throughout the data set and would be difficult to delineate.
accurate to approximately ±2-3m data, though much of the data was better than this.
Ground truth applied: 97% data meets CatZoc C

13. Antigua SDB Trial SDB attributes: Good coverage
Good horizontal accuracy
Limited to ~15m depth
Lesser depth accuracy than MBES, SBES and leadline, however 97.7% data within CATZOC C requirements
Conclusion from Antigua SDB dataset
Within its limitations it can provide useful information for the mariner

14. The Cartographic Question
Important to get across uncertainty to the user
Need some indication to the mariner as to how they should behave… SDB is not a self contained dataset, its merits may be relative to surrounding data.
Eg. preferable for mariner to go through SDB rather than sparse leadline data…?
Is existing symbology enough?

15. The Mariner’s perspective
Usergroup Engagement
The Mariner’s perspective

16. Establishing rules for representation on the chart
Usergroup Engagement
Establishing rules for representation on the chart
Outline of options presented to mariner test group (not dwelling upon this!)

17. The Mariner’s perspective
Usergroup Engagement
The Mariner’s perspective
Mariner has limited interest in how surveys are conducted, “that is UKHO’s job”
Didn’t want more ‘clutter’ on the face of the chart
No more symbology
The general opinion was that they would like to know where SDB survey data is used on a chart, but there was a preference not to use any additional symbology. There was a preference to use the source diagram
no requirement to differentiate soundings derived from satellite
bathymetry on the chart face itself.

18. Integrating with many other information sources
Chart Compilation
Integrating with many other information sources
How SDB is considered as apart of chart compilation process

19. Chart Compilation
New shoal depths found from SDB, not in original leadline survey
Existing depths confirmed and repositioned for greater horizontal accuracy
However… unconfirmed leadline shoal depths retained
Example of how compiled chart benefited from SDB dataset

20. Accuracy of contouring improved
Chart Compilation
Accuracy of contouring improved
Example of how compiled chart benefited from SDB dataset

21. BA2066
Southern Antigua
Proudly announcing UKHO’s first published used of SDB on New Edition of BA2066. How SDB is communicated to end user

22. ENC Representation S-57 Standard for ENCs
Tightly defined cartographic representation
Existing S-57 attribution can already accommodate SDB data
CATOC = C
Data may be further qualified by object class
M_QUAL sub-attribures as follows:
POSACC = 10m
SOUACC = 3m
TECSOU = 11 “satellite imagery”
Demonstration of how SDB already fits within the existing S-57 attribution schema

23. Conclusions & Implications
for future charting
Antigua chart not necessarily definitive way of representing SDB in future
Limited control still required
Currently SDB seen as a way of complementing & extending new MBES surveys… where conditions make this practical
Building experience … growing confidence?
Consider these as first baby steps…

24. WorldView-2 Satellite imagery credit: © DigitalGlobe, 2013
Thank you
WorldView-2 Satellite imagery credit: © DigitalGlobe, 2013