Ocean Optics: Fundamentals & Naval Applications Technical Training Short Course Sampler

Ocean Optics: Fundamentals & Naval Applications

Instructor:
Jeffrey H. Smart

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My Background in Ocean Optics
(some dates are approximate)
1988-1996: Environmental Specialist for Active Optics Project

• Acquire and learn how to use multi-spectral radiance/irradiance sensor system, optical
backscatter sensors, and beam transmissometers
• Develop software to provide analysis products such as optical attenuation profiles vs.
wavelength
• Test experimental systems to “measure” nighttime “K”
• Participated in 5 major sea tests plus numerous smaller sea tests
• Write environmental summary reports on temporal & spatial variability

1992-1994: Environmental Specialist for MIW Program

• Deploy multi-spectral radiance /irradiance sensor system, optical backscatter sensors,
and beam transmissometers in shallow coastal sites off Panama City & off Ocean City,
Md
• Write environmental summary reports on short-term temporal variability (< 1 week) at
fixed sites

My Background in Ocean Optics
(some dates are approximate)

1994 to 1997: Project Manager & PI for bio-optical monitoring system
• Analyze & document results for sensors
• Analyzed data from associated platforms

1996-2010: Environmental Specialist for active optics program

1995 to present: Proj Mgr/PI for ONR World-wide Ocean Optics Database (WOOD)

2001-2003: Littoral Warfare Advanced Development (LWAD)

• Project Scientist in the Yellow Sea supporting hyper-spectral optics system
• Environmental expert for several sea tests, including exercise in East China Sea

Various Naval Applications of Ocean Optics
• Mine Warfare:
- Sonar systems are typically used to find Mine-like Objects
- Electro-Optical Identification (EOID) sensors are used to classify those
objects
- Examples of EOID systems*:
- Areté Associates Streak Tube Imaging LIDAR (STIL) system
- Northrop Grumman Laser Line Scan (LLS) system
- Raytheon LLS system

• Special Operations Forces
– Detectability of SEAL Delivery Vehicles
– Detectability of submerged divers

• Underwater Communications
– Optical properties of water directly impacts range & quality of transmission

• Port Security & Anti-Submarine Warfare (ASW)
– Passive Detectability
– Active (e.g. Laser) Detectability

• Other Possible Application: Bathymetry Mapping

* Ref: “Electro-optic Identification Research Program,” James S. Taylor, Jr. and Mary C. Hulgan, Fifth International
Symposium on Technology and Mine Problem, 22-25 Apr 2002, Monterey, CA

Airborne Mine Countermeasures (AMCM)
• The MH-60S, fitted with Airborne Mine Countermeasures (AMCM) made its
first flight in July 2003.

• Lockheed Martin Systems Integration… is integrator for the MH-60S mine
countermeasures systems which includes:
– Raytheon Airborne Mine Neutralization System (AMNS) with BAE Systems
Archerfish expendable underwater vehicle that destroys the mines;
– Northrop Grumman Rapid Airborne Mine Clearance System (RAMICS), a non-towed
mine neutralization system that will clear near-surface and surface-moored mines
using a Kaman Aerospace laser target sensor and a 30mm mk44 gun;
– Raytheon AN/AQS-20A towed sonar with mine identification system which entered
production in September 2005;
– Northrop Grumman airborne laser mine detection system, AN/AES-1 ALMDS,

• AN/AES-1 ALMDS detects and classifies floating and near-surface moored
mines, using pulsed laser light. The ALMDS pod is mechanically attached to
the MH-60S with a standard Bomb Rack Unit 14 (BRU-14) mount.

Ref: http://www.naval-technology.com/projects/mh_60s/

Airborne Laser Mine Detection System
(ALMDS)
Operations Desert Storm and Desert Shield
demonstrated the need for minehunting systems as
an integral element of deployed forces. …Navy began
developing …five airborne mine countermeasure
systems to negate the identified threat. One of the
systems, the Airborne Laser Mine Detection
System (ALMDS), is a mine countermeasure that is
intended to detect, classify, and localize floating
and near-surface moored sea mines. The Navy will
deploy the ALMDS on MH-60S helicopters to provide
organic airborne mine defense for Carrier Battle
Groups (Carrier Groups), and Amphibious Ready
Groups (Amphibious Groups).…Areté Associates is
contracted with Northrop Grumman to provide the
STIL* sensor for the ALMDS system. The STIL
sensor detects sea surface and near sea surface
volume mines that the AN/AQS-20X system is not
designed to detect.

* STIL = StreakTube Imaging Lidar

Airborne Mine Neutralization System (AMNS)

• Raytheon is receiving $14.7M for seven more
AMNS systems
• Ref: info by Jeff Steelman via email from George
Pollitt, 9-23-10

…. The airborne mine neutralization system will
explosively neutralize bottom and moored
mines using an expendable mine neutralize
device. The system will be deployed from the
MH-60 helicopter as part of the littoral combat
ship mine countermeasures mission module.

EOID Sensor Systems
The EOID laser line scan technology uses a diode-pumped Nd: YAG laser that provides 500 mW
of power for the Raytheon system and 160 mW for the Northrop Grumman system, both
operating at 532 nm wavelength. The Raytheon system was a research and development
sensor maintained and operated by CSS while the Northrop Grumman system was sized to fit
into the AN/AQS-14A(V1) towed body. The laser illuminates a small spot, which is synchronously
scanned by a photomultiplier receiver to build up a raster-scanned image. The laser scans
downward through a 70-degree field-of-view (FOV). Figure 1 represents the EOID scanning
scheme for target identification.

Variability in c 532 nm
Best  Middle

Worst
0 /m 1.0 /m

Example of How Optical Values Affect Imagery

Ref: Smart,J.H., “Optical Climatologies for US Navy Missions,” Mine Warfare, April 2002

Airborne Mine Neutralization System
(AMNS):

uses “Archerfish” UUV controlled via fiber-
optic link to helo; UUV has sonar & optical
sensors

Conceptual View of How uses “Archerfish”

Safe standoff ~xxyds (horizontal)

•Daylight operations only
Target Environment
•<Xft by YftR AOU •<Xkt wind speed
Hover •No false cues •<X sig wave height
Altitude •mean period?
FO for •Vert/horiz motion?
(XXft) ACS/Video
•Diam: XX – YY ft •<Xkt current
and C2
ACS tracking of NTR by
LHS Depth LHS for navigation Case Depth
(XXft) 0-XX’

3.5km of FO for
ACS/Video and C2

Water Depth > XXft

•NTR trajectory for re-acquire?
•NTR trajectory for endgamge?

•Re-acquire involves acoustic detection of case
•Endgame could involve detection of mooring

“To acquire the target, Archerfish activates its short range sonar and video link,
transmitting sonar imagery and video pictures back to its controller for inspection
and identification. The advanced maneuvering capabilities enable it to traverse the
target to obtain images from a variety of angles providing the controller with
detailed identification information.
Following confirmation of target, Archerfish is maneuvered in place where the mine
is detonated…”

http://www.baesystems.com/ProductsServices/bae_prod_2.html

AN/ASQ-235 Airborne Mine Neutralization System (AMNS)

CSTRS w/ AMNS Jettison Testing

LHS with Neutralizers

Common Console

Final
Neutralize Approach Reacquire

Common Neutralizer
(Expendable & Exercise)

Transit to
Uncertainty Area
Identify

Steps to Target Neutralization
Reported Location
Operational
Standoff
Launch & Transit 350m Actual Location
1 Reacquisition
Search
Neutralize Target
Area(RSA)
6 Safe Depth Valid
Safe Standoff valid
4,5,6 Pilot Master ARM valid
Neutralizer
3 SO ARM valid
Track SO FIRE sent
4 Way Points 2
shown Water
Current

1 Safe Standoff
250m

Launch Point

2 Reacquire MLO 3 Final Approach 4 Identify MLO 5 Maneuver to Neutralize
Achieve Safe Depth valid

Safe Standoff valid
Safe Standoff valid Safe Standoff valid Safe Depth valid Safe Depth Valid
Safe Standoff valid SO ARM sent
ARM Timers complete Pilot Master ARM sent

Testing Highlights
• High Current at Carderock CWC (Nov-Dec
05)
– 77 Runs at various water speeds up to
Maximum
– Estimated Successful Prosecutions: 92%
• At-Sea CT Testing (15 Dec 05 - 21 June
06)
– Performed Successful Attack Runs against
all Target Types in Shallow and Deep
Target Fields.
– 43 Missions Against Targets
• MH-53 CT / DT Flight Tests (28 July – 15
Aug 06)
– 26 Missions Against Targets
– Total Average Ts (All Targets) = 7m 13s

Special Operations (SPECOP) Forces

• Possible Concerns:
-Detection of underwater light sources used by SPECOP forces:
-Light sticks were developed by the U.S. Navy as an inconspicuous and
easily shielded illumination tool for special operations forces dropped
behind enemy lines. Besides their use as children's toys, they are also
used extensively as a navigation aid by divers searching in muddy
water. The light sticks glow as a result of the energy released by a
chemical reaction.
Ref: http://www.articlesbase.com/education-articles/importance-of-chemiluminescence-and-bioluminescence-
2075376.html

- Detection of bioluminescence from SEAL Delivery Vehicle or swimmers

ASW Applications:
Daytime Passive Optical Detection

Example of Hull Detectability from Airborne
Observer

November Yellow Sea
Chinese sub

Src: unknown

Example of Hull Detectability from
Airborne Observer

Src: http://www.militaryphotos.net/forums/showthread.php?164653-Submerged-submarines

19

Passive Optical Hull Detection

• Problem:
– Submarines operating
at shallow depths in
clear littoral waters
can be visible to an
airborne observer
• Mitigation Approach:
– Install COTS optical
sensors to monitor
water clarity +
detectability models =
predict of vulnerability
to visual detection
Src: http://media.photobucket.com/image/photo%20of%20submerged%20submarine/cbleyte/submarine_submerged_visible.jpg
20

Passive Optical Hull & Surface Wake
Detection
Visual Detection
Submarines operating at or near the surface are potentially vulnerable to visual
detection. Anything that protrudes above the surface, such as a periscope,
antenna, or mast will leave a significant wake if the submarine is moving at any
speed over a few knots. And, since depth control and steerage is quite difficult at
low speeds, it is not uncommon for submarines to be traveling at least 4 or 5
knots just below the surface.
The periscope (for example) will create a wake, called "feather", which is quite
visible, and will also leave a remnant of its passage, called a "scar". The scar is a
long streak of foam or bubbles left behind after the object passes. The feather
may be just a few meters, but the scar may be tens of meters long. Either may be
visible for up to 10 miles, and are easily spotted by low flying aircraft in the
vicinity.
Periscopes and other protruding masts and antennas are also often painted in
dark or camouflage colors to reduce their visibility.
If the water is especially clear, the submarine hull or its shadow may be visible for
a few hundred feet under water, but is usually not distinguishable unless the
water is shallow with a light colored bottom (like white sand).

Src: see notes page

21

Factors Affecting Visual Detection

Sun Angle

Altitude, Look Angles, Dwell Time

Clouds
Haze
Surface Clutter

Target Depth Water Clarity
Target Reflectance Water Reflectance

Bottom Depth
Bottom Reflectance

Factors Affecting Detectability
• Primary environmental factors influencing optical hull detection
– Water clarity
– Sea state
– Atmospheric conditions (especially cloud cover &
fog)
– Illumination
• Primary operational factors influencing optical hull detection
– Submarine depth
– Hull contrast
– Proximity/altitude/angle/training of observers
– Period of exposure
• Secondary factors
– Bottom contrast

Example of Underwater Visibility

Src: http://www.militaryphotos.net/forums/showthread.php?164653-Submerged-submarines

Diver visibility range & attenuation

ln CL From Radiative Transfer Theory,
visibility range ( m ), V = − • Priesendorfer (1976)
c • Duntley (1963)
CL contrast detection limit for human being
c optical beam attenuation coefficient (m-1)

4.8
V=
[1.18c(650) + 0.081]
Accuracy better than 10%

Backscattering is NOT a
good proxy for visibility

Zaneveld and Pegau (2003)

Other Possible ASW Applications:
Nighttime Passive Optical Detection due
to Bioluminescence

Bioluminescence:
Why Should the Navy Care?

• Complements acoustics - does not replace it

• Prevalent in the acoustically noisy littorals where
boats must operate shallow

• Many initial submarine detections are by non-
acoustics

Factors Affecting
Bioluminescence Detectability

Signature Intensity
• Platform Speed
• Platform Depth
• Bioluminescence Potential
• Water Clarity

Summary of Concept Demo
on US Submarine
• Photometer successfully collected
Bioluminescence intensity while a USS
Submarine was underway
• Could distinguish night/day Bioluminescence in
signatures, even without validated time stamps
• Could distinguish higher/lower Bioluminescence
based on depth of Submarine

What is Bioluminescence:
An optical parameter

• Emission of light by living organisms
• Turbulence initiated chemical reaction
• Globally distributed phenomenon
– est. 70% of marine organisms bioluminesce
– measured from equator to Arctic pack ice
• Blue-green in color which travels furthest
in the ocean

All images, Harbor Branch (E. Widder)

UNCLASSIFIED

What causes these
organisms to glow?

Bioluminescent organisms can be
mechanically stimulated to
produce light. Turbulence
generated by a ship’s passage or
even the movement of dolphins
and fish is enough to create the
glow.

UNCLASSIFIED

UNCLASSIFIED

Does it matter? Those cells are so small.

The luminescence of a single
dinoflagellate is readily visible
to the dark adapted human eye.
Most dinoflagellates emit about
6 e+8 photons in a flash lasting
only about 0.1 second.
Much larger organisms such as
jellyfish emit about 2 e+11
photons per second for
sometimes tens of seconds.

Bioluminescence
You don’t have to be a large target to be vulnerable to
detection by bioluminescence.
Figures show low light level camera detection of a 10 in.
diameter sphere at different depths.

Depth = 10 ft. Depth = 20 ft.

Optical Clarity

• The clarity of the water depends on multiple factors
and varies depending on depth, location, currents,
outflow from rivers to name a few factors.
• Objects may be vulnerable due to color and
configuration. If the target has a high contrast
against the background it is more likely to be
spotted.
• In clear, shallow areas where bottom reflectance is
high (e.g., white sand, light colored coral), vertical
(downward) detection of relatively dark objects will
be enhanced due to contrast.

Yellow Sea, East China Sea, & Philippine Sea: Historical Optical Clarity
Vertical (left) & Horizontal (right) Visibility
•Turbid in coastal areas, very clear offshore
•Straits high spatial and temporal variability, with vertical
visibilities from 5-30 ft. Values can be artificially low due
to shallow bathymetry off the west coast of Taiwan.
•Vertical visibility 40-80+ ft offshore
•Vertical visibility 0-10 ft coastally
•Summer rainy season, clearer waters in winter months
6-10
m
3-6
m
0-1
m
1-2 6-10
m m
~6-15 m

•Most turbid of the 4 areas, most historical data
available
•Dominated by tidal cycle, coastal waters very dirty
•Vertical visibility 20-40+ ft in deeper waters
•Vertical visibility 0-10 ft in all coastal areas ~15-30
•Summer rainy season, clearer waters in winter months m

South China Sea and Philippine Sea
Historical Optical Clarity/Vertical Visibility
•Very clear waters in all of Philippine Sea
•Vertical visibilities 30-80+ ft throughout
•Minimal effects of tides and summer rainy
season
•More turbid pockets around Northern
Philippine Islands, but generally very clear with
little variability

~12-15 m

•Least historical data available of 4 areas
•Highly turbid along northern boundaries, much
clearer offshore
•Vertical visibilities 40-60+ ft offshore in deep waters > 10 m
•Vertical visibilities 0-20 ft coastally
•Summer rainy season, clearer waters in winter
months
•Clear waters around Philippines and further south

Other Possible Applications:
Bathymetry Mapping in Shallow Coastal Waters

Bathymetry from Ocean Color
• Knowledge of ocean bathymetry is important for navigation & for
scientific studies of the ocean's volume, ecology, and circulation, all
of which are related to Earth's climate.
• In coastal regions detailed bathymetric maps are critical for storm
surge modeling, marine power plant planning, understanding of
ecosystem connectivity, coastal management, and change analyses.
• Because ocean areas are enormously large and ship surveys have
limited coverage, adequate bathymetric data are still lacking
throughout the global ocean.
• Satellite altimetry can produce reasonable estimates of bathymetry
for the deep ocean [Sandwell et al., 2003, 2006], but the spatial
resolution is very coarse (∼6–9 kilometers) and can be highly
inaccurate in shallow waters, where gravitational effects are small.
• Depths retrieved from the ETOPO2 bathymetry database for the Great
Bahama Bank are seriously in error when compared with ship
surveys & no statistical correlation was found between the two
• Determining a higher-spatial-resolution (e.g., 300-meter) bathymetry
of this region with ship surveys would require ~ 4 years of nonstop
effort.

Ref: Lee, Z., et.al., "Global Shallow-Water Bathymetry From Satellite Ocean Color Data,” EOS, Transactions American
Geophysical Union, VOL. 91, NO. 46, P. 429, 2010, doi:10.1029/2010EO460002

Bathymetry from Ocean Color

Fig. 1 (a) Depth of {he Great Bahamas Bank retrieved from the E70P02 bathymetry database. (b) Scatter
plot between in situ depth and E70P02 bathymetry of matching locations (inset shows ETOP02
bathymetry under 60 meters). (c) bottom depth derived from Medium Resolution Imaging Spectrometer
(MER/S) measurements (14 December 2004) by the hyper-
spectral optimization process exemplar (HOPE) approach. (d) like Figure I b, a scatter plot between in situ
depth and M£RIS depths (rounded to nearest integer to match ETOPO2 format; blue indicates 14
December 2004,green indicates 6 September 2008). The coefficient of determination (R2) represents all
data points (281) in the plot. Note the color scale difference in Figures 1a and Ic. Black pixels represent
land or deep waters.

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Ocean Optics: Fundamentals & Naval Applications Technical Training Short Course Sampler

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