Underwater photogrammetry 
HN 116 — 06/2020 
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by bundle adjustment over all Included observa 
tions. 
Mapping underwater structures using 
photogrammetrlc technlgues as the only acquisi 
tion method, or as part of a multi-sensor system, 
has been widely performed In tasks such as reef 
monitoring (Fabrl et al. 2019), Inspection of ship 
hulls (Kim and Eustlce 2013) or cave surveying 
(Nocerlno et al. 2018). Ship wrecks were observed 
and modelled by Prado et al. (2019) by fusion with 
MBES data. Further examples of photogrammetrlc 
wreck surveys, mostly In relatively clear water con 
ditions, can be found In Drap et al. (2015) or Nomes 
et al. (2015). 
Fig. v. Plan view of a io cm raster of the MBES sounding data set of the wreck. 
Colour coding depicts depth 
2 Methodology 
This paper presents data from a campaign carried 
out by BSH and Jade University of Applied Scienc 
es, surveying a sunken former German air force 
vessel from WWII, 25 m In length and about 4 m 
In width. The wreck Is located at a depth of about 
14 m (relative to NHN) In the Bay of Neustadt (Bal 
tic Sea). The MBES data was collected from the 
hydrographic survey vessel VWFS Deneb, operat 
ed by BSH. A ROV egulpped with a camera to ac- 
gulre Imagery for photogrammetrlc analyses was 
subseguently deployed from the vessel. The re 
sulting point cloud was fused with the MBES data 
In order to georeference the photogrammetrlc 
Imagery. 
2.1 Multibeam echo sounder data set 
The MBES data set was collected from Deneb using 
a Teledyne-Reson Seabat 7125-SV2 (400 kHz) with 
512 beams per swath. The software Teledyne PDS 
was used for real-time data acgulsltlon and guallty 
control. Five survey lines were collected over the 
wreck, three In the west-east direction and two In 
the north-south direction. The data was further 
post-processed using Teledyne-CARIS HIPS & SIPS. 
Fig.,..], shows the 0.10 m depth raster generated 
from the sounding data over and In the vicinity 
of the wreck. The wreck consists of about 71,866 
points over an area of 203.5 m 2 
The total sounding uncertainty was calculated 
based on all estimated and measured uncertainty 
sources and propagated to the 3D position of the 
soundings. The soundings comprising the wreck 
have an uncertainty of 15 cm at the 95 % confi 
dence level. 
2.2 ROV and imagery data set 
The ROV observations were carried out with a 
SAAB SeaEye Falcon ROV ®.g ; .2, left). The ROV has 
a depth rating of 300 m and Is capable of carrying 
up to 8.5 kg of additional payload. As the on-board 
ROV-camera did not provide sufficient resolution 
and stability for these photogrammetrlc analyses, 
an additional Industrial-grade Easier Ace camera 
was mounted In a pressure housing on top of the 
Fig. 2: ROV equipped with camera system on top (left) and camera in pressure housing (right) 
ROV ©.g...2, right). Relevant technical specifications 
are summarised In Table© and Table 2. 
The camera housing was egulpped with a 
hemispherical port to reduce Image degradation 
Introduced by the optical properties of water. 
These Include mainly refraction and dispersion 
as a perfectly centred port would eliminate these 
effects completely and work as an additional lens 
element In the ray path. Deviations due to Imper 
fect fitting of the dome can mostly be compen- 
Saab SeaEye Falcon 
Maximum depth 
300 m 
Forward speed 
> 3 kn 
Weight 
55 kg 
Dimensions 
moo mm X 6oo mm x 500 mm 
Maximum added payload 
8.5 kg 
Table i: ROV specifications 
Basler Ace acAig2o-48gc 
Sensor size 
9.2 mm x 5.8 mm 
Resolution 
1920 px X 1200 px 
Maximum frame rate 
50 Hz 
Pixel pitch 
4.8 pm x 4.8 pm 
Focal length 
4.8 mm 
Table 2: Camera specifications