3. BASIC HYDROGRAPHY - MODULE 1 3
TOPICS
● Basic understanding of why we need standards
and specifications?
● Basic understanding of the statistical terms
used in the NAMRIA Standards for
Hydrographic Surveys in reference to the IHO
Standards for Hydrographic Surveys (S-44)
● Knowing the standards and specifications of
each class of Survey “Order”.
4. BASIC HYDROGRAPHY - MODULE 1 4
Why Standard?
Hydrographic technologies and requirements are
continually evolving, as is the expanding
community of users. In order for the
hydrographers to have uniformity in acquired
hydrographic data, thus the need for a Standard.
Such acquired data will be used for the
production of navigational charts which are used
by mariners globally.
Why do we need Standards for Hydrographic Surveys?
5. BASIC HYDROGRAPHY - MODULE 1 5
Standards for Hydrography
“something set up and established by
authority as a rule for the measure of
quantity, weight, extent, value or
quality”
The primary (but not only) standard for
hydrographic data is the International Hydrographic
Organization's (IHO) Special Publication 44 (S44),
currently in it’s sixth edition.
6. BASIC HYDROGRAPHY - MODULE 1 6
What is a Standard?
“Standard” implies something which can be
used as a basis for comparison, such as a
model or a set of rules.
7. BASIC HYDROGRAPHY - MODULE 1 7
What is a Specification?
A specification is an exact statement of the particular needs
to be satisfied
A specification tells us how a standard is to be met and
interpreted, and how the item will be measured to ensure
the standard is met.
8. BASIC HYDROGRAPHY - MODULE 1 9
IHO Standards for
Hydrographic Surveys
S-44 6th Edition
S-44 is the IHO’s minimum standards
to standardize the survey quality
between member states
… ‘for the execution of hydrographic
surveys for the collection of data …
used to compile navigational charts …
for the safety of surface navigation
and the protection of the marine
environment’
9. BASIC HYDROGRAPHY - MODULE 1 10
S-44 is a standard, NOT a specification. It is used either
directly by IHO member state organizations or as the
basis of national nautical charting specifications.
S-44 is not mandatory for non-governmental
organizations.
10. BASIC HYDROGRAPHY - MODULE 1 11
How S-44 describes its standards?
IHO Standards For Hydrographic Surveys (S-44) uses these
statistical terms to standardize:
● Hydrographic survey quality
● Errors
● Accuracy
● Precision
● Uncertainty
● Confidence interval
● Resolution
11. BASIC HYDROGRAPHY - MODULE 1 12
Definition of Terms
Error
“The difference between an observed or computed value of a quantity
and the ideal or true value of that quantity.” Errors can be categorized
as systematic or random errors.
Accuracy
“The extent to which a measured or enumerated value agrees with the
assumed or accepted value”
Precision
“The degree of refinement of a value; not to be confused with
ACCURACY, which is the degree of conformance with the correct value.”
12. BASIC HYDROGRAPHY - MODULE 1 13
High Accuracy, High Precision Medium Accuracy, Low Precision
Low Accuracy, Low Precision Low Accuracy, High Precision
13. BASIC HYDROGRAPHY - MODULE 1 14
Definition of Terms
Uncertainty
“a statistical assessment of the likely magnitude of the error.”
Confidence Level
“The probability that the true value of a measurement will lie within the
specified uncertainty from the measured value. In Normal Distribution
of Error, the 95% confidence level for 1D quantities (e.g. depth) is defined
as 1.96 x standard deviation; and the 95% confidence level for 2D
quantities (e.g. position) is defined as 2.45 x standard deviation”
14. BASIC HYDROGRAPHY - MODULE 1 15
Definition of Terms
Resolution
“The separation by an optical system of parts of an object or of two
or more objects close together. The degree of ability to make such
a separation, called RESOLVING POWER, is expressed as the
minimum distance between two objects that can be separated. The
degree of ability of a radar set to indicate separately the echoes of
two targets in range and bearing.
15. BASIC HYDROGRAPHY - MODULE 1 16
To harmonize the conduct of
hydrographic surveys within
NAMRIA and concerned
stakeholders, NSHS is
adopted by virtue of AO No.
001 s 2019 dated 25 Mar
2019.
16. BASIC HYDROGRAPHY - MODULE 1 17
How to Achieve the Standards?
● Quality Control and Quality Assurance (Best Practices)
● Effective Survey Planning
● Reconnaissance Survey
● Acceptable Survey Speed
● Offsets and Calibration
● Environmental Factors
● Survey Records
● Other Mitigating Factors
17. BASIC HYDROGRAPHY - MODULE 1 18
Different Hydrographic Survey Orders
Why do we have different survey Orders?
Depends on the importance of under keel clearance and
objects under water that will affect surface shipping, different
survey specification and standard are applied to different areas,
namely:
1. Exclusive order
2. Special order
3. Order 1a/1b
4. Order 2
19. BASIC HYDROGRAPHY - MODULE 1 21
Standards to be Met
For each class of “Order”, it has different standards that must be
met:
1. Total Horizontal Uncertainty - THU
Refers to 95% Confidence Level
Soundings on the seabed must be positioned within the following limits:
Exclusive Order: 1m
Special Order: 2m
Order 1a / 1b: 5m + 5% of Depth
Order 2: 20m + 10% of Depth
20. BASIC HYDROGRAPHY - MODULE 1 22
Standards to be Met
2. Total Vertical Uncertainty - TVU
Refers to 95% Confidence Level
Soundings on the seabed must have an overall depth uncertainty within
the following limits:
Depth Uncertainly Standards
Where
a= portion of the uncertainty that does not
vary with depth.
b=a coefficient which represents that portion
of the uncertainty that varies with depth
d=depth
b x d=the portion of the uncertainty that
varies with depth
Exclusive Order Special Order
Order 1A/1B Order 2
21. BASIC HYDROGRAPHY - MODULE 1 23
Standards to be Met
3. Full Seafloor Search
Required for Exclusive, Special Order and Order 1a
● Because under keel clearance is critical or under water features are of
concern to surface shipping
● Need swath bathymetry system of MBES (or possibly SBES combined
with SSS) to achieve this
22. BASIC HYDROGRAPHY - MODULE 1 24
Standards to be Met
4. Feature detection:
Underwater features that shall be detected
Exclusive Order: >0.5m
Special order: >1m
Order 1a: >2m when depth <40m
Order 1b: Not required
Order 2: Not required
23. BASIC HYDROGRAPHY - MODULE 1 25
SUMMARY
“Without standards,
there can be no
improvement.”
