Title:

Speakers:

Date:

7 & 8 December 2020

Organisers: Supported by:

Satellite-derived bathymetry: Overview and the demand of guidelines in quality assurance

Assoc. Prof. Dr. Poerbandono, ITB Bandung Dr. Thomas Heege, EOMAP Seefeld

Captain Dr. Oke D. Pribadi, Pushidrosal Jakarta

Depth and bathymetry

Charted depth

SEABED

Low WaterCD

Depth points

Triangular Irregular Network

Depth is the vertical separation between a point on the seabed and the sea surface.

− Depths on nautical charts refer to Chart Datum (CD).

3-dimensional surface model

High Water

Gridded depth data

2-dimensional surface model,i.e. contours

3-dimensional surface model

SURFACE

Bathymetry is the geometrical representation (model) of seabed surface generated from depth points.

Data acquisition in shallow water areas

Various means of depth data acquisition,including SDB being one of the so-calledoptical methods:

Accurate and widely

used. Subject to

coverage and risks.

Fast and reliable.

Subject to

economic scale.

Echosounder LiDAR SatelliteSimple and low-

cost. Subject to

limitations.

Depth accuracy

Position accuracy

Seafloor coverage

SDB offers outstanding horizontal accuracy, but requires improvements in vertical accuracy and its assurance procedures

200

800

600

400

1000

0

2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

862

289314

143 144

Growth and trend

In Indonesia internet resources (i.e. news, exposure, event, research) regarding the application of SDB are growing.

− Imagery:

− Accuracy:

− Max. depths:

− Methods:

Sentinel 2A, Landsat 8, WorldView 2/3, Pleiades, SPOT

0.25 m to 6.27 m

2 m to 40 m

band-ratio, machine learning, physics-based

e.g. SBES

MSL, LWL, CD, N/A

0% or some 6% to 75%

− Calibration:

− Datum:

− Training data:

3

Common aspects in SDB

applications

0

1

2

3

4

5

6

7

0 10 40 50

4,56

0,65

6,27

1,071,77

0,510,54

Bel itung~1m

Claimed accuracy

Root-mean square errors (RMSE) is almost always used as measure of accuracy.− Use of TVU is also reported, i.e. % of compliance.

4

Semak Daun

Tj. Priok

1,91 Morotai

G. Iyang

~2.46m

G. Matra

M orot ai

G. Mat ra

Se mak Daun

Se mak Da un

Semak Da un

Tj. Priok

20 30Max. depth (m)

RM

SE(m

)

Range of RMSE

Sources: Dewi et al 2019, Jaelani & Putri 2019, Setiawan et al 2019, Meliala et al 2019, Muhammad et al 2020, Meliala et al 2020, Lumban-Gaol et al 2020, Dewi et al 2020

Application: Detection of shoalsChart Number 318 - South of Teluk Bone

Readings:− IHO B-11

(IHO-IOC GEBCOCook Book)

− IHO S-4

SDB has been useful to identify shoals.− Distinct presentation (of SDB origin) on chart is

required.

5

Depth Contour

Source: Pushidrosal

Imagery

Application: Shoals on chartsChart No. 373 Plan 3 - Pulau-pulau Takabonarate; Pulau-pulau Pasitelu

With SDB, chart is updated.

6

Before After

Source: Pushidrosal

Assuring quality: Satellite data

Correction of environmental impacts on satellite data→ Increasing data quality*

Levels of QA procedures*:

− Data evaluation - suitable imagery, reliable external QA/QC

− Data processing -

Simple: Band-ratios, regional calibration, machine learning

Advanced: Physical corrections on heterogeneous error sources

Integrated: Maximize degree of environmental corrections, highest independency and transparency, and highest data integration (i.e. multiple satellite imagery, external data assimilation and consistency check, error propagation and error forecast)

7*for all data points, also those without external data availability (majority of satellite data points)

products are subject of heterogeneous (error) sources: atmosphere, sea-state, turbidity, seafloor,

n , …

Accuracy assessment of depth data

Assuring quality: Error assessments

Data and each of the step in the workflow contribute to total uncertainty.

8

Imagery

In-situ depth

Training/calibration Generation of depth points

Contouring of depth

Accuracy assessment of surface model

Total uncertainty is accumulated in the final product, i.e. bathymetric map.

Closing remark

Uncertainties are contributed by:

− Satellite recording conditions

− Data analysis procedures

− In-situ depth data

− Data calibration/training

− Generation of depth points

− Generation of bathymetric contours

Concerns:

− Time of acquisition

− Vertical datum

− Tidal correction

− % and distribution of sample for training/calibration

− Correction level of environmental conditions: benthic cover, water column turbidity, …

− Integration level of data sources and data processing

9

Guidelines are required in assuring quality of SDB.