Remote measurement of chlorophyll concentrations to determine extent of water pollution is discussed. Construction and operation of radiometer to provide measurement capability are explained. Diagram of equipment is provided

Arvesen, J. C.

Millard, J. P.

Weaver, E. C.

English

NASA Technical Reports Server

October 1972	 B72-10568 
NASA TECH BRIEF S
Ames Research Center
	 -4r 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Assessment of Water Pollution by Airborne
Measurement of Chlorophyll 
Airborne methods for detection of pollution in 
natural bodies of water primarily are based on meas-
urement of changes in water color. The color changes 
may yield information on the location and extent of 
Light Chopper	 Reference Filter 
IcqJ 
Detector 
Split Fiber-
Optics Bundles	 Sample Filter 
algal blooms, the intensity of silting, and the distribu-
tion of chemical effluents. However, specific pollut-
ants can not be sensed directly; for example, nitrates, 
phosphates, mercury compounds, or DDT can not be 
sensed, but it may be possible to infer the presence 
of nutrient or toxic substances by studies of their 
effects on the color of a body of water. 
Photosynthesis is the common link in the marine 
and land food chain, and it is the only significant 
process by which solar radiation is converted into 
life-supporting substances. In bodies of water, regions 
of photosynthetic activity are associated with sur-
rounding areas of zooplankton and marine life; how-
ever, as the level of nutrients increases, or if the dis-
persal and flushing action of the body of water is low, 
photosynthesis may create dense growths of algae 
which can have a severe impact on other marine life.
All methods for measuring the rate of photosyn-
thesis in a water body require contact of a sensor 
with the water, or that certain measurements be made 
on the water. However, since all major photosynthetic 
processes require the presence of chlorophyll, and it 
has been established that there is a correlation be-
tween chlorophyll mass and primary productivity in 
marine surface waters, the concentration of chloro-
phyll can be used directly as an indicator of basic 
biological processes and as a delineator of the extent 
and effects of water pollution. Hence, remote meas-
urement of chlorophyll concentrations provide valu-
able insight for pollution studies. 
An airborne chlorophyll correlation radiometer has 
been devised to measure the chlorophyll content of 
water bodies such as freshwater lakes and estuaries 
as well as extended coast lines which characteristically 
exhibit interaction of plumes from rivers and bays 
with ocean water. As indicated in the diagram, the 
radiometer consists of an entrance fiber-optics bundle 
split into two parts, an optical chopper, sample and 
reference filters, and a photomultiplier tube with S-10 
response characteristics. A phase-lock amplifier phased 
by a signal from the optical chopper permits com-
parison of the intensity of the sample and reference 
light bundles at a frequency of 1 kHz, and an auto-
matic gain control system compensates for variations 
in the intensity of sunlight falling on the body of 
water. 
The radiometer is mounted on an aircraft so that 
it can have a downward look at the surface of the 
body of water. The radiometer output represents the 
intensity of upwelling sunlight in the spectral region 
(continued overleaf) 
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centered about 443 nm with reference to the region 
centered at about 525 nm, and laboratory tests have 
demonstrated that the radiometer output is related to 
the chlorophyll content of water. The simultaneous 
determination of water surface temperature is also 
desirable inasmuch as many water outflows and pro-
cesses associated with the introduction of nutrients or 
pollutants can also appear as differences in water 
temperature. A commercially available radiometer is 
used to obtain airborne indications of temperature. 
The ability to make measurements quickly from an 
aircraft over a large area and to have the results 
available immediately for real-time analysis make the 
technique described above especially useful for pollu-
tion studies.
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: TSP 72-10566 
Patent status: 
NASA has decided not to apply for a patent. 
Source: John C. Arvesen, Ellen C. Weaver, 
and John P. Mifiand 
Ames Research Center 
(ARC-10648) 
B72-10566	 Category 04


Assessment of water pollution by airborne measurement of chlorophyll

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