Credit: Cecile Rousseaux/USRA/NASA

100° W

50° W

0°

50° E

100° E

150° EThe color of an object is actually the color of the light reflected while all other colors
are absorbed. Most of the light that is reflected by clear, open ocean water is blue,
while the red portion of sunlight is quickly absorbed near the surface. Therefore,
very deep water with no reflections off the sea floor appears dark navy blue. Near
the Bahama Islands however, where the water is clear but also shallow, sunlightis reflected off white sand and coral reefs near the surface, making the water
appear turquoise.

45° N

0°

45° S

75° S

0123410-3PgC y-1x(petagrams COVERAGEof carbon per year)
SPECTRALOCEAN COLOR HERITAGE SENSORS compared with PACE

This true color image of the North Atlantic Ocean was created using datafrom the Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi
National Polar-orbiting Partnership satellite collected on April 12, 2015.
Notice the swirling phytoplankton eddies and different color coastal waters
associated with runoff from the eastern United States.

VISIBLE
Atmosphericcorrection /MODIS
chlorophyllflourescence
Atmosphericcorrection(clear ocean)Atmosphericcorrection(coastal)***MODIS on Terra does not yet provide science-quality ocean data**MODIS/VIIRS short-wave infrared bands are not optimized for oceans

5 nanometer resolution (345 - 885 nm), 26 required multispectral bands

ULTRAVIOLETPRODUCTSSHORT-WAVE
NEAR
INFRARED INFRARED

Cover image:

SHORT-WAVE NEARINFRARED INFRARED

Find more information at http://pace.gsfc.nasa.gov.
Credit: NASAN O M E AS U R E M E N TS

PRODUCTS

Total pigment or
Chlorophyll-aVISIBLE

This graph compares the portions of the electromagnetic spectrum
that the PACE Ocean Color Instrument will observe compared toprevious NASA ocean color sensors. Human eyes are adapted
to see a narrow band of this spectrum called visible light. Usingsatellite sensors to detect multiple spectral band combinations,scientists can study various aspects of ocean color in ways thatthey cannot from a photograph. Ocean color features, clouds,
and aerosols each leave their signatures in the electromagneticspectrum and scientists can observe and analyze these patterns
to detect changes.

VIIRS(2011-)

3 bands

CZCS
SeaWiFS MODIS(1978-1985) (1997-2010) (2002-)*

Ocean Color Heritage Sensors compared with PACEPACEULTRAVIOLET

Spectral Coverage

Absorbing aerosols
Dissolved organics
Functional groups
Particle sizes
Physiology
Pigment
fluorescence
Coastal biology
Atmosphericcorrection(clear ocean)Atmosphericcorrection(coastal) &Aerosol/cloudproperties

What isColor theOcean

There are many places on Earth where water is not deep or clear, and therefore,
not always blue. Suspended particles and dissolved material in water increase
the scattering of light and absorb certain wavelengths differently, influencing thecolor of the water. For example, phytoplankton are microscopic marine plants thatuse chlorophyll and other light-harvesting pigments to carry out photosynthesis.
Chlorophyll is a green pigment that absorbs
the red and blue portions of the light spectrum
and reflects green light. Ocean water with highconcentrations of phytoplankton can appear
as various shades of green, depending upon
the type and density of the phytoplankton
population. Other types of algae can makewater appear reddish or deep yellow. Near
Sediment-laden water (brown and tan) pours
coastal areas, dissolved organic matter, suchinto the northern Gulf of Mexico from theas decaying plants, can produce a yellow or
Atchafalaya River in this image taken on
brown color. Soil runoff produces a variety ofApril 7, 2009.
yellow, red, brown, and gray colors.
Credit: NASA

The image at right shows a harmful algal bloom in Florida
on July 2, 2016. The bloom was caused by cyanobacteria,
but not all cyanobacteria blooms are toxic.

Deep, clear, open ocean water appears darknavy blue [top right], while shallow coastal waters
surrounding islands can appear turquoise dueto the reflection of white sand and coral reefs
on the ocean surface [middle and left].
Credit: NASA

Smelly algae blooms as thickas guacamole closed Atlantic
beaches, polluted lakes andrivers, and could even be
seen from space in summer
2016. If you wanted to surf or
go fishing in affected areas,
you were out of luck.

Phytoplankton are the foundation of the aquatic food web, the primary
producers, feeding everything from microscopic, animal-like zooplankton
to multi-ton whales. Small fish and invertebrates also graze on theplant-like organisms, which are eaten by larger marine animals and so on.
Like land plants, phytoplankton consume carbon dioxide and produce
oxygen during photosynthesis. In fact, phytoplankton created about half
the oxygen we breathe today. Phytoplankton are extremely diverse, varying
from photosynthesizing bacteria (cyanobacteria), to plant-like diatoms, toarmor-plated coccolithophores (drawings not to scale).
Credit: NASACredit: NASAcyanobacteria

diatomdinoflagellate

green algae

coccolithophore

Credit: NASAWhy is Ocean Color Important?

For more information, visit:www.nasa.gov/earth

The high spectral resolution of PACE will
enable scientists to distinguish phytoplankton
types, which will hopefully help to identify
harmful algal blooms from space one day.

Credit: U.S. JGOFS• ocean health and water quality to assist
resource managers.

National Aeronautics and Space Administration

NP-2016-7-458-GSFC

Credit: Kai Schumann, NOAA National Ocean Service• the storage of carbon in the ocean and the roleof the ocean in Earth’s climate; andNASA Sets the PACE for Advanced Studies of Earth’s Changing Climate
http://pace.gsfc.nasa.gov

www.nasa.gov

Phytoplankton can be the harbingers
of death or disease. Certain speciesof phytoplankton produce powerfultoxins, making them responsible forharmful algal blooms, sometimes
called red tides. Toxic blooms cankill marine life and people who eat
contaminated seafood.

During photosynthesis,
phytoplankton consume
carbon dioxide on ascale comparable toland plants. Some ofthis carbon is carried
to the deep ocean
when phytoplankton
die and sink, andsome is transferred
to different layersof the ocean as
phytoplankton
are eaten by othercreatures, whichthemselves generate
waste and die. Worldwide,
this biological carbon pumptransfers about 10 gigatonnes ofcarbon from the atmosphere to the deep ocean each year. Even smallchanges in the growth of phytoplankton may affect atmospheric carbon
dioxide concentrations, which feed back to global surface temperatures.

Scientists use ocean color data to study:• fundamental questions about phytoplankton
blooms, the aquatic food web, and fisheries;

www.nasa.gov

Measuring Ocean Color: At Sea and From Space
Scientists can measure ocean color directly—by taking water samples from ships and permanent observation sites—or indirectly—using Earth-observing satellites that measure the amount of light backscattered and reflected from Earth’s
surface at various wavelengths. Unlike patchy ship-based measurements, satellites provide continuous global coverageover long timescales. NASA’s Coastal Zone Color Scanner (CZCS) operated from 1978 through 1986, and was the firstsatellite ocean color mission and provided a proof-of-concept despite its limited view. The first dedicated global ocean color
sensor, Sea-viewing Wide Field-of-view Sensor (SeaWiFS), operated from September 1997 until the end of the mission inDecember 2010. Today, NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) instrument onboard theAqua satellite (launched in May 2002) and the Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National
Polar-orbiting Partnership (NPP) satellite (launched in October 2011) routinely observe ocean color along with ocean color
satellites operated by other countries.

BEACHCLOSED

Phytoplankton growth depends on theavailability of sunlight and nutrients. Whenconditions are favorable, phytoplankton
populations can grow at a rate fasterthan they are consumed, a phenomenon
known as a bloom. Phytoplankton blooms
may cover hundreds of square kilometers
and are easily visible from space. In
this image, ocean waters glow peacockgreen off the northern Namibian coaston November 21, 2010. Phytoplankton
blooms often occur along coastlines
where deep, nutrient-rich waters well up from the ocean depths. The lightcolor of this ocean water suggests the calcite plating of coccolithophores isturning the water milky.

Credit: NASA150° W

Spectrophotometry is a method to measure how much light a water
sample absorbs by measuring the intensity of light that passes throughthe solution. The diagram illustrates how a spectrophotometer works.
Credit: NASACan we tell if a bloom is toxic
from space? Not yet. Water
quality managers use ocean
color satellite data to decide
where to take water samples
to measure for toxins.

To continue the eighteen-year record of ocean color measurements,
NASA plans to launch the Plankton, Aerosol, Cloud, ocean
Ecosystem (PACE) mission in 2022. The Ocean Color Instrument(OCI) onboard PACE will provide the most advanced, continuous
global observations at high-spectral resolution from the ultraviolet(UV) to near infrared (i.e., 350 – 800 nanometers), plus several
short-wave infrared (SWIR) bands. PACE’s broad spectral coverage
will unveil a variety of new products to aid our understanding of theocean as well as the atmosphere. Over the ocean, UV data will help
discriminate between living and non living components of the upperocean. Visible wavelengths will be used to identify the compositionof phytoplankton communities.

Remote Sensing of Ocean ColorRrs (sr -1)

Coupled with ship-based measurements and computer models,satellite data allow scientists to observe and study different
characteristics about the ocean and how they have changed
over time, as well as predict how they might change in the future.
This false-color image [right], generated using the NASA Ocean
Biogeochemical Model, shows the primary production by diatoms,a group that tends to be large and contributes heavily to the global
carbon cycle. Primary production reflects the amount of carbon thatis converted using sunlight from carbon dioxide into organic carbon
through a process called photosynthesis. The organic carbon
represents the carbon that will be usable by higher trophic levels.
These data help to improve our understanding of the global ocean
carbon and biogeochemical cycles.

What Color is the Ocean?

Diatoms(remote sensing reflectance)

Modeling Phytoplankton

0.025
0.02

Near IR
0.015
0.010.0050400500600700800900

Wavelength (nm)Clear Water

Phytoplankton

Colored Dissolved
Organic Matter

Weathered Rock Particles
Suspended Sediments

Ship-based optical instruments on ocean-going
research vessels are often lowered into the water
on a cable.
Photo credit: Joaquin Chaves, Ocean Ecology Lab Field Support Group,NASA’s Goddard Space Flight Center

Scientists use a technique similar to spectrophotometry to quantify ocean color remotely. Satellite instruments(such as OCI) measure light reflected back to the satellite at different wavelengths and create emission
spectra graphs [inset, top right]. Differences in the shape of the spectra can be used to determine what is in
the water, such as sediments (orange line), chlorophyll (green line), or clear water (blue line). Brighter objects(e.g., sediments) reflect more light of all wavelengths while darker objects absorb more, thus the values arehigher across the spectrum for sediment.
Credit: NASASimple
Spectrophotometer
Activity

1.
2.
Credit: NASA

3.

Prepare four, square containers of water. One container should contain only clear water. For the other three containers:
Put one drop of blue food dye in one, one drop of green food dye in another, and some tea (no leaves) in the last.
Mix each container well.

8.

Build a light sensor with battery + power + orange wire + sensor + number display—see Materials Guide.

Circle the highest sensor value for each colored water sample in Table 1. Do you notice a pattern?

Calculate the percent of light transmitted for each colored water sample in Table 2. To do this, divide eachcolored water sensor value from Table 1 by the clear water sensor value for the corresponding light color andmultiply that value by 100 to get the percentage of light transmitted. For example, (blue water sensor value forblue LED light) ÷ (clear water sensor value for blue LED light) x 100 = (percentage of blue light transmitted).
Calculate and record each percentage in Table 2.

Table 2
Put together a light source with power + bright LED. Make sure you have three properly tuned* LED lightsources (blue, green, red).
* Tune one LED light to red (tune up “r” with the littleBitsTM screwdriver, tune down “g” and “b”), tune one LED
to green (tune up “g,” tune down “r” and “b”), and tune one LED to blue (tune up “b,” tune down “r” and “g”).
Make sure the LED light is not too bright. To do this, adjust the three light sources and/or the sensitivity of thedetector so that the light sources put out distinct colors and read up to 98 when transmitted through clear water.
Keep the same settings for the entire experiment.

4.

*Note that a laboratory spectrophotometer is more sensitive than the one used in this activity.

Sample% of Blue lighttransmitted% of Green lighttransmitted

Clear water(clear water sensor
value for blue LED light) ÷(clear water sensor value forblue LED light) x 100 = 100% of Red lighttransmitted(clear water sensor(clear water sensor
value for green LED light) ÷value for red LED light) ÷(clear water sensor value for (clear water sensor value forgreen LED light) x 100 = 100 red LED light) x 100 = 100

Blue water
Attach the light sensor to one side of the black base and place the blue LED light source on the opposite side ofthe black base. The light source should be level with (and shining directly on) the light sensor on the opposite sideof the black base.
Green water

5.
6.

Put the clear water sample into the black base and turn on the blue LED light so that the blue light shines throughthe container of clear water and is received by the light sensor on the opposite side. Cover the spectrophotometer(black base, light sensor, and light source) and water sample with a black cloth to minimize background light.

Record the value on the light sensor (received by the blue LED light) for clear water in Table 1. Remove the blueLED light. Insert the green LED light and record the value on the light sensor for clear water in Table 1. Remove
the green LED light. Insert the red LED light and record the value on the light sensor for clear water in Table 1.
Repeat for all colored water samples (blue, green, tea), completing Table 1.

SampleSensor Valuefor Blue LED light

Sensor Valuefor Green LED light

Sensor Valuefor Red LED light

The color of the water affects how much light from the light source is transmitted or absorbed before reaching the lightsensor. Specifically, the spectrum (i.e., graph) for each colored water sample demonstrates that the highest
percentage of light transmitted through a medium corresponds most closely to the color of its constituents while
the other colors are absorbed. In other words, the blue water transmits the highest amount of blue light and absorbs
green and red light. Likewise, the green water spectrum peaks at green and the tea water spectrum peaks at red.
These are called spectral signatures. While ocean color satellite sensors measure reflected light—not light that istransmitted across a water sample like a spectrophotometer does—scientists are able to remotely sense the samespectral signatures, allowing them to observe and analyze changes in ocean color.

Materials Guide• littleBitsTM components or their equivalents:		

- 2x battery + cable

http://littlebits.cc/acc*essories/battery-plus-cable			- 2x power bit

http://littlebits.cc/bits/littlebits-power			- 3x rgb LED

http://littlebits.cc/bits/rgb-led			- 3x wire

http://littlebits.cc/bits/wire-bit			- 1x light sensor

http://littlebits.cc/bits/light-sensor			- 1x number output

http://littlebits.cc/bits/number-plus• Two 9V batteries

9.

Plot the values from Table 2 on the Graph for all three colored water samples (blue, green, red) using threecorresponding colored pencils (blue, green, red).

• Four square, clear containers of clean tap water• Blue and green food dye• Cooled tea

10. Discuss the results revealed in Table 2 and the Graph.

Table 1Results

Tea water• Three colored pencils: blue, green, red• CalculatorGraph• Black cloth to cover water sample andminimize ambient light• A black base into which the square watercontainers fit. You should be able to secure theLED light(s) on one side of the base and thelight sensor directly across—see photo below
Note: A simple Lego® structure is used.

10090

Clear waterBlue water

Green water

Light transmitted (%)

In this activity, you will use an inexpensive,simple spectrophotometer* to test how
light at different visible wavelengths(blue, green, red) is transmitted, or absorbed, through four different colored water
samples. Clear water is used as the “control,” characterizing the light source andnormalizing the other samples. The blue water represents the open ocean water withfew plants—conditions you might find far from land in the middle of the ocean. Thegreen water represents productive water with a high concentration of phytoplankton,i.e., a phytoplankton bloom. The tea water represents coastal water or river outflow
that contains decaying organic material such as leaves.

7.

Setup and Investigation

80
70
60
50
40
30
20Credit: NASA

10Tea water0Blue

Green

Color of lightRedReference:
Schollaert Uz, S. 2016. Building intuition for in-water optics and ocean color remote sensing:Spectrophotometer activity with littleBits™.
Oceanography 29(1):98–103, http://dx.doi.org/10.5670/oceanog.2016.01