John Lekki, Robert Anderson, Quang-Viet Nguyen, and James Demers

Glenn Research Center, Cleveland, Ohio

George Leshkevich

National Oceanic and Atmospheric Administration, Great Lakes Environmental Research Laboratory, Ann Arbor, Michigan

Joseph Flatico and Jun Kojima

Ohio Aerospace Institute, Brook Park, Ohio 

Development of Hyperspectral Remote Sensing 

Capability For the Early Detection and Monitoring 

of Harmful Algal Blooms (HABs) in the Great Lakes

NASA/TM—2013-217447

May 2013

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John Lekki, Robert Anderson, Quang-Viet Nguyen, and James Demers

Glenn Research Center, Cleveland, Ohio

George Leshkevich

National Oceanic and Atmospheric Administration, Great Lakes Environmental Research Laboratory, Ann Arbor, Michigan

Joseph Flatico and Jun Kojima

Ohio Aerospace Institute, Brook Park, Ohio 

Development of Hyperspectral Remote Sensing 

Capability For the Early Detection and Monitoring 

of Harmful Algal Blooms (HABs) in the Great Lakes

NASA/TM—2013-217447

May 2013

AIAA–2009–1978

National Aeronautics and

Space Administration

Glenn Research Center

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NASA/TM—2013-217447 1

Development of Hyperspectral Remote Sensing Capability For 

the Early Detection and Monitoring of Harmful Algal 

Blooms (HABs) in the Great Lakes

John Lekki, Robert Anderson, Quang-Viet Nguyen, and James Demers

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

George Leshkevich

National Oceanic and Atmospheric Administration

Great Lakes Environmental Research Laboratory

Ann Arbor, Michigan 48108

Joseph Flatico and Jun Kojima

Ohio Aerospace Institute

Brook Park, Ohio 44142

Abstract

Hyperspectral imagers have significant capability for detecting and classifying waterborne

constituents. One particularly appropriate application of such instruments in the Great Lakes is to detect 

and monitor the development of potentially Harmful Algal Blooms (HABs). Two generations of small 

hyperspectral imagers have been built and tested for aircraft based monitoring of harmful algal blooms. In 

this paper a discussion of the two instruments as well as field studies conducted using these instruments 

will be presented. During the second field study, in situ reflectance data was obtained from the Research 

Vessel Lake Guardian in conjunction with reflectance data obtained with the hyperspectral imager from 

overflights of the same locations. A comparison of these two data sets shows that the airborne 

hyperspectral imager closely matches measurements obtained from instruments on the lake surface and 

thus positively supports its utilization for detecting and monitoring HABs.

Introduction

Two generations of small lightweight Hyperspectral Imaging Systems have been developed by 

engineers at the National Aeronautics and Space Administration (NASA) Glenn Researwch Center (GRC) 

and the Ohio Aerospace Institute (OAI). The systems consist of a pushbroom hyperspectral imager, a 

point spectrometer, a three axis inclinometer, a Global Positioning System (GPS) receiver and a data 

acquisition and control computer. Both generations of Hyperspectral Imagers (HSI) are sensitive in the 

visible and near infrared portion of the spectrum. The point spectrometer is included to measure incident 

solar irradiance and also is used to measure atmospheric effects. The three axis inclinometer and GPS 

receiver are included to record the position and attitude of the sensor so that the hyperspectral data can be 

georeferenced.

Science Background

NASA Glenn Research Center and the National Oceanic and Atmospheric Administration (NOAA)

Great Lakes Environmental Research Laboratory (GLERL) are collaborating to utilize an airborne 

hyperspectral imaging sensor suite to forecast and monitor Harmful Algal Blooms (HABs) in the western 

basin of Lake Erie and Saginaw Bay in Lake Huron. The HABs can be very dynamic events. They often 
NASA/TM—2013-217447 2

form, spread and then disappear within a 4 to 8 week time period in late summer. They are a concern for 

human health, fish and wildlife because they commonly contain a potentially toxic algae, Microcystis.

Microcystis can contain the toxin microcystin. In the Great Lakes one of the most common forms of 

microcystin is Microcystin-LR, which also happens to be one of the most toxic forms of microcystin.

Because of this potential toxicity there is a need for the blooms to be detected early and continually 

monitored. 

In the U.S., the Great Lakes are the single most important aquatic resource from an economic, 

geographic, international, ecological, and societal perspective. The Great Lakes represent the largest 

supply of surface freshwater in the world. Combined, the lakes cover an area of over 94,000 mi2

(245,000 km2

) and contain 5,400 mi3 (23,000 km3) of water. The Great Lakes contain about 18 percent of 

the world's surface freshwater supply and over 80 percent of the U.S. supply (Ref. 1). The Great Lakes 

coastline of 6,700 mi is the nations longest and provides over 500 beaches for recreational activities. 

Unlike other coastal waters, the Great Lakes provide drinking water to over 40 million U.S. and Canadian 

citizens so water quality (as well as water security) is thus an important concern for the region. The Great 

Lakes provide about 56 billion gallons of water daily for municipal, agricultural, and industrial use. The 

region’s 60 million people place significant demands on this water resource for drinking water, 

transportation, recreation, food production, and manufacturing.

One of the threats to water quality in the Great Lakes is Microcystis aeruginosa, which is the 

dominant bloom-forming, toxic cyanobacterium occurring in the Great Lakes. Microcystis aeruginosa 

produces a suite of cyclic heptapeptide hepatotoxins, known as microcystins—the most important of 

which is microcystin-LR. Microcystis has (again) become a dominant component of the summer 

phytoplankton in both Saginaw Bay and western Lake Erie. Moreover, preliminary studies have verified 

the presence of the cyanotoxin, microcystin, in both systems (Refs. 2, 3, and 4). As such, the recent 

expansive blooms of Microcystis have caused considerable concern due to aforementioned dependence on 

these waters as a resource and the health risks attributable to microcystins. 

This resurgence of nuisance cyanobacteria (and apparent selection for one dominant taxon) has been 

attributed to the long-term effects of massive populations of non-indigenous zebra mussels. The mussels 

promote the blooms of toxic Microcystis through selective rejection of the pseudo-feces during the 

filtration process (Refs. 3, 5, and 6). Because of the establishment of large populations of non-indigenous 

mussels in many regions of the Great Lakes, it has been predicted that Microcystis will establish summer 

dominance in mesotrophic/eutrophic regions (Ref. 5).

Because of the increased incidence of cyanobacterial blooms in these important freshwaters systems 

and the public health concerns attributable to microcystins, much attention has been given to Microcystis 

blooms and associated toxins within important water resources. Despite very limited studies, relatively 

high concentrations of microcystin have been found in Saginaw Bay, western Lake Erie, and in the

western region of Lake Ontario (Refs. 2, 3, and 4). In 1995, microcystin concentrations in Saginaw Bay 

and western Lake Erie exceeded the World Health Organization’s limit of 1 μg/L for drinking water 

(based on microcystin-LR) (Refs. 3 and 7). Microcystin concentrations were measured at 3.5 mg/L in 

Saginaw Bay in July 1995, and estimated to be as high as 24 mg/L in western Lake Erie in September 

1995 (Ref. 3). In a shallow harbor in western Lake Ontario, microcystin concentrations were as high as 

400 mg/L in the summer of 2001 (Ref. 4).

Algal blooms can be very dynamic events, changing significantly day to day. Monitoring such events 

with even high resolution satellite data is not suitable by itself because such data does not have the 

temporal resolution (owing to infrequent repeat pass coverage) needed to monitor the quickly changing 

blooms. These events are well suited for complementary aircraft based monitoring because the blooms are 

dynamic and they can spread over a large area.
NASA/TM—2013-217447 3

TABLE 1.—COMPARISON OF MONITORING METHODS

Observation

method

Observation 

frequency

Resolution

Satellite

Landsat TM Once every 8 days 30 m

Satellite

MODIS 2/day 1 km

Satellite

MERIS Every 2 to 3 days 300 m

Satellite

SeaWiFS 1/day 1 km

Research Vessel 

In situ Flexible Point

Aerial Monitoring Hourly 1 to 5 m

The added value of aerial monitoring may be seen in the comparison shown in Table 1 between the 

various ways in which the algal blooms can be monitored. In situ sampling provides many high accuracy 

physical measurements at a point or a group of points. Satellites can provide measurements over a large 

area but the frequency of observation can be low for high resolution imaging. Aerial Monitoring is,

therefore, complementary because of better control over the frequency and resolution of measurements 

which is important as we attempt to understand rapidly changing blooms. With aerial monitoring, lower 

concentrations are potentially detectable because of higher spatial and spectral resolution. Also, using 

aircraft allows the quick locating of areas of interest and the guiding of in situ sampling to areas of high 

interest even under cloud cover. Tailoring instrumentation to suit a particular problem is easier with 

aircraft than with satellites since the satellite instrumentation is not accessible once the satellite is 

launched.

Hyperspectral Imaging Suites

Generation I Hyperspectral Imager Sensor Suite

A multidisciplinary team of researchers, scientists, engineers, and technicians from GRC, NOAA 

GLERL and the Ohio Aerospace Institute have in a very short time period of 8 months, designed, 

developed, integrated, and flight tested a highly specialized suite of instruments for aerial water quality 

measurement. The suite of instruments consists of a GRC designed point spectrometer, a GRC-designed 

hyperspectral imager, a commercial-off-the-shelf (COTS) GPS receiver, a COTS three axis gyroscopicstabilized inclinometer, and a GRC-designed data acquisition system. The GRC hyperspectral imager 

obtains wavelength-resolved images of the lake in narrow 2 nm wide bands of light. The hyperspectral 

imager wavelength range is 400 to 900 nm, thus allowing 250 distinct spectral bands. The resulting threedimensional data block consists of a stack of images from the imager acquired as the aircraft passes over 

areas of interest. The point spectrometer significantly adds to the capability of the instrument suite 

because it can provide highly accurate measurements of the incident solar radiation as well as 

measurements of the atmospheric water vapor content. This combined sensor suite provides accurate 

spectral radiometric measurements of the lake constituents, which will translate into an ability to detect 

lower concentrations of pollutants and harmful algal blooms.

The entire suite of instruments weighs less than 2.3 kg and uses less than 15 W of power. This makes 

the package very flexible in terms of the aircraft that it can be deployed on. Because of the instrument 

flexibility the team was able to mount the instrument, shown in Figure 1, on the avionics door of a T 34 

aircraft and obtain the desired data in a very cost effective manner. The environmentally-sealed 

instrument package uses three windows to provide optical access and is mounted on the T 34 avionics bay 

door with a forward-facing aerodynamic fairing.
NASA/TM—2013-217447 4

Figure 1.—The instrument package mounted on the T-34 avionics bay 

door. The three optical windows face downward (not shown). The 

external enclosure measures approximately 8- by 10- by 4-in. thick.

2006 Field Operations Using the Generation I HSI

During September 2006, the formation of a significant algae bloom in the Kelly’s Island area of Lake 

Erie and a second smaller bloom that formed in Maumee Bay were observed. On August 17, HSI data 

was acquired at the same time that GLERL took in situ measurements. The data that we acquired on 

September 5 was not accompanied with water sampling but satellite data from the MODIS instrument on 

Terra was available for comparison.

During the August 17 and September 1, overflights of western Lake Erie no blooms were visible. A 

photograph, in Figure 2, shows that there were areas that did have a deeper green appearance on 

September 1. Four days later, on September 5, another overflight was conducted, and on this day algal 

blooms, shown in Figure 3, were observed. These series of observations show that the formation of algal 

blooms can be very dynamic.
NASA/TM—2013-217447 5

Figure 2.—Picture of a forming algal bloom on September 1. Algal coloration is visible 

in Lake Erie Western Basin near the Bass Islands. The algae looks to be very 

cohesive and does not mix well with the sediment.

Figure 3.—An open water bloom west of Middle Bass Island on September 5, 2006.
NASA/TM—2013-217447 6

An image of the Lake Erie area, shown on Figure 4, taken from a satellite on September 5 is directly 

comparable to the HSI data taken on the same day. An enlargement of the area around the Lake Erie 

islands is shown in Figure 5. This enlargement contains the blooms that were photographed in Figure 3. It 

can be seen that because the resolution is approximately 500 m, it is very difficult to tell where the 

blooms were present, which is shown in the yellow box in Figure 5.

Figure 4.—Image from MODIS Terra on September 5, 2006.

Figure 5.—Enlargement of the Lake Erie island area from the September 5, 

2006, Terra image shown in Figure 4. The yellow box shows the 

approximate location and extant of the hyperspectral data shown Figure 6

and Figure 7.
NASA/TM—2013-217447 7

Figure 6.—Hyperspectral Image of algal bloom centered at 532 nm.

Figure 7.—Hyperspectral image of algal bloom centered at 723 nm.

However, the HSI data as seen in Figure 6 and Figure 7, which approximately covers the area in the 

yellow box on Figure 5, clearly shows the algal bloom. An airborne HSI very nicely compliments data 

obtained from a satellite. While it is not as easy to cover the area shown in Figure 4 with an aircraft, it is 

also not possible to observe small, but important formations, such as those shown in Figure 6, with low to 

moderate resolution satellite data. With higher spectral and spatial resolution it should be significantly 

easier to detect the onset of an algal bloom with an aircraft based HSI than is possible with existing 

orbital assets. Note that the two images of the algal bloom in Figure 6 and Figure 7 illustrate that the 

bloom has different reflectivity at different wavelengths.
NASA/TM—2013-217447 8

Generation II Hyperspectral Imager

A second generation HSI for aerial water quality measurement has been designed, developed, 

integrated and flight tested. This hyperspectral imager also operates as a part of a suit of instruments.

These instruments have been used to obtain spectral measurements of algae in the western basin of Lake 

Erie and also in Lake Huron’s Saginaw Bay during 2007. The entire suite of instruments also consists of a 

GRC designed point spectrometer, the GRC designed second generation hyperspectral imager, a COTS 

Global Positioning Receiver, a COTS three axis inclinometer, and a data acquisition system. The second 

generation hyperspectral imager obtains images of the lake in very narrow bands of light, less than 

2.5 nm. The wavelength span that the HSI covers is approximately 400 to 900 nm. As in Generation I,

250 distinct spectral bands are available resulting in a three-dimensional data block consisting of a stack 

of images from the imager acquired as the aircraft passes over areas of interest. The internal optics of the 

second generation imager have been significantly changed and a cooled imager has replaced the uncooled 

imager in the first generation. These changes have resulted in a dramatic improvement in the signal-tonoise ratio over the first generation imager.

The entire suite of instruments weighs less than 10 lb and uses less than 100 W of power. The second 

generation imager takes advantage of a modular design. The front lens can be changed to modify the field 

of view and resolution of the instrument. Also the imager can be changed if higher speed or greater light 

sensitivity is required. This makes the package very flexible in terms of the platform on which it can be 

deployed.

2007 Field Operations

The second generation imager was flown in conjunction with a monitoring cruise of the R/V Lake 

Guardian, an EPA vessel, shown in Figure 8. During this cruise, water samples and radiometric 

measurements were made of the lake at multiple locations, shown in Figure 9. The radiometric 

measurements made from the Lake Guardian included spectral measurements of downwelling irradiance 

and water leaving radiance. From the ratio of the water leaving radiance and downwelling irradiance a 

spectral reflectance was obtained. In order to compare the capability of the aircraft HSI to accurately 

measure water reflectance, the HSI measurements were compared to the in situ measurements. The three 

data points where in situ measurements will be compared to airborne measurements are denoted as points 

885, 1131 and e59 in Figure 9.

Figure 8.—In this picture the EPA ship R/V Lake Guardian is seen from the NASA Lear 25 during the concurrent 

operations in 2007.
NASA/TM—2013-217447 9

Figure 9.—Map of the 2007 water sampling locations in western Lake Erie. The points surrounded by 

boxes are points where optical measurements were made from the ship.

Figure 10.—Plot of the downwelling irradiance for September 13. The 8:49 and 10:24 plots are both 

direct measurements. The 10:43 plot is an extrapolated value derived from the two solar irradiance 

measurements that were made earlier in the day. 

In order to obtain reflectance data from an airborne instrument, which measures radiance, the 

irradiance must be known and also the effects from atmospheric scattering and attenuation must be 

accounted for. The in situ irradiance measurements, shown in Figure 10, are used in conjunction with the 

airborne radiance measurements to obtain the airborne reflectance values. In this case the irradiance as 

Downwelling Irradiance

0

20

40

60

80

100

120

300 400 500 600 700 800 900

Wavelength (nm)

Irradiance (uw/cm2/nm)

8:49

10:24

10:43
NASA/TM—2013-217447 10

measured from the R/V Lake Guardian at 10:24 can be used in conjunction with the aerial radiance 

measurement of point 885 as the aerial measurement happened at 10:25. For the aerial measurements of 

points 1131 and e59, which occurred at 10:43, there is not a similarly timed in situ measurement of 

irradiance. In this case the measured values of irradiance at 8:49 and 10:24 have been extrapolated to 

obtain an estimated irradiance for 10:43.

The atmosphere significantly affects the light gathered by the HSI. Not only does it include light 

reflected from the lake but light is also gathered that has been scattered by the atmosphere in between the 

aircraft and the lake. Furthermore, atmospheric constituents attenuate the light reflected from the lake 

through absorption and scattering. In order to correct for these effects, measurements at multiple altitudes 

have been made to characterize the atmospheric effects. These measurements were conducted at 300 ft

and again at the nominal altitude of 10,500 ft. The measurements were made of the same location at these 

two altitudes. The location that was chosen was in the middle of the lake over deep water. This location 

provided the most uniform target available. By taking measurements from low altitude and high altitude 

of the same location, the effects of the atmosphere are directly obtained. To further correct for the 

atmospheric effects from ground level to 3000 ft the previously measured atmospheric effect from 3000 

to 10,500 ft was extrapolated to account for the first 3000 ft. This measurement technique was used to 

correct for the atmospheric effects and obtain a more precise estimate of the water leaving spectral 

radiance.

The spectral reflectance plots of the three points, shown in Figure 11 to Figure 13, show good 

qualitative agreement between reflectance measured at the surface and the airborne measurement. In 

Figure 11, it is shown that the in situ measurement location was covered by the HSI overflight. In this 

case, the in situ measurement was taken on the day after the overflight, so a comparison of the reflectance 

magnitudes is not valid. It is highly probable that the constituents in the water did not change appreciably 

as there was no significant lake disturbing weather between the time of the overflight and the time of the 

in situ measurement. In general the spectral reflectances are very similar. The reflectance peaks at 560 

and 700 nm, which are characteristic of chlorophyll A, agree in both measurements. Also the absorption 

peak at 620 to 630 nm, which is characteristic of phycocyanin (Ref. 8), agrees in both measurements. The 

major difference between the two measurements is that the airborne measurement appears to be relatively 

too high in the blue portion of the spectrum, near 400 nm. It is believed that this is caused by additional 

light from atmospheric scattering that has not been corrected for.

A comparison of the data obtained for point 1131 is shown in Figure 12. In this case both of the 

measurements were made on the same day and the in situ sample point was captured within the HSI data.

Here the data shows general agreement with a spectral reflectance profile characteristic of chlorophyll A.

Neither plot shows an absorption peak that is characteristic of phycocyanin. The magnitude of the 

reflectance is fairly close for both measurements. They appear to have a general difference of about 

0.002 percent which is within 7 percent of full scale. The only major difference is that the airborne 

measurement reflectance again is much higher than the in situ measurement near 400 nm.

The data for point e59 is shown in Figure 13. In this case, the in situ measurement point fell outside 

of the hyperspectral data area by about 150 m so a detailed comparison is probably not appropriate.

However the lake constituents probably did not change too drastically in this distance so general 

observations are appropriate. Both reflectance measurements are fairly close in terms of magnitude. Also, 

both spectra have reflectance peaks characteristic of chlorophyll without a clearly identifiable absorption 

peak characteristic of phycocyanin. As in the previous three measurements the big difference between the 

two spectra is an increased reflectance measured in the blue by the airborne instrument.
NASA/TM—2013-217447 11

Figure 11.—Data acquisition locations and reflectance spectra for point 885. 

(Top) The area covered by the HSI overflight is outlined. The water sample point 

falls within the area and is indicated by the blue cross. Hyperspectral data is 

taken from the same point denoted by blue triangle. (Bottom) Two spectrographs 

are shown. The red graph is the reflectance spectrum measured on the water 

from the EPA vessel R/V Lake Guardian. The graph in black is the reflectance as 

measured by the hyperspectral imager from overflight on the same day. 
NASA/TM—2013-217447 12

Figure 12.—Data acquisition locations and reflectance spectra for point 1131.

(Top) The area covered by the HSI overflight is outlined. The water sample point 

falls within the area and is indicated by the blue cross. Hyperspectral data is 

taken from the same point denoted by blue triangle. (Bottom) Two spectrographs 

are shown. The red graph is the reflectance spectrum measured on the water 

from the EPA vessel R/V Lake Guardian. The graph in black is the reflectance as 

measured by the hyperspectral imager from overflight on the same day. 
NASA/TM—2013-217447 13

Figure 13.—Data acquisition locations and reflectance spectra for point e59. 

(Top) The area covered by the HSI overflight is outlined. The water sample point

falls outside the HSI area and is indicated by the blue cross. In this case the 

overflight did not cover the water sample location so Hyperspectral data is taken 

from the nearest HSI data point denoted by blue triangle. (Bottom) Two 

spectrographs are shown. The red graph is the reflectance spectrum measured 

on the water from the EPA vessel R/V Lake Guardian. The graph in black is the 

reflectance as measured by the hyperspectral imager from overflight on the same 

day. 
NASA/TM—2013-217447 14

Conclusion

Two generations of airborne hyperspectral imagers have been developed and tested. The instruments 

have been designed to be compact and operate on a low power budget so that they are appropriate for 

many airborne platforms especially unmanned aerial vehicles and high altitude balloons. The primary 

application of the instruments was to demonstrate the capability of early Harmful Algal Bloom detection 

by detecting various concentrations of the pigment phycocyanin as an indicator. The second generation 

Hyperspectral Imager (HSI) was used to gather data in conjunction with waterborne measurements. In 

general the airborne measurements show very good agreement with the in situ measurements. The largest 

area of variance is in the HSI showing a higher reflectance of blue light than the in situ measurement.

This is considered an issue with atmospheric correction and this, along with continued study into the 

sensitivity of the HSI for identifying phycocyanin pigment, will be the subjects of further study.

References

1. Great Lakes National Program Office, The Great Lakes: An Environmental Atlas and Resource Book,

United States Environmental Protection Agency, Chicago, Illinois and Governmental of Canada, 

Toronto, Ontario, Third Edition, 1995.

2. Brittain, S.M., Wang, J., Babcock-Jackson, L., Carmichael, W.W., Rinehart, K.L. and Culver, D.A.,

“Isolation and characterization of microcystins, cyclic heptapeptide hepatotoxins from a Lake Erie 

strain of Microcystis aeruginosa,” J. Great Lakes Res., Vol. 26, 2000, pp. 241–249.

3. Vanderploeg, H. A., Liebig, J. R., Carmichael, W. W., Agy, M. A., Johengen, T. H., Fahnenstiel, G. 

L., and Nalepa, T. F., “Zebra mussel (Dreissena polymorpha) selective filtration promoted toxic 

Microcystis bloom in Saginaw Bay (Lake Huron) and Lake Erie,” Canadian Journal of Fisheries and 

Aquatic Sciences, Vol. 58 No. 6., 2001, pp. 1208–1221. 

4. Murphy, T.P., K. Irvine, J. Guo, et al.. “New microcystin concerns in the lower Great Lakes,” Water 

Quality Research Journal of Canada, Vol. 38, No.1, 2003, pp. 127–140.

5. Raikow, D. F., “Food web interactions between larval bluegill (Lepomis macrochirus) and exotic 

zebra mussels (Dreissena polymorpha),” Canadian Journal of Fisheries and Aquatic Sciences. Vol. 

61, No. 3, 2004, pp. 497–504. 

6. Nicholls, K. H., Heintsch, L., and Carney, E., “Univariate Step-trend and Multivariate Assessments of 

the Apparent Effects of P Loading Reductions and Zebra Mussels on the Phytoplankton of the Bay of 

Quinte, Lake Ontario,” J. Great Lakes Research, Vol. 28, No. 1, 2002, pp. 15–31.

7. World Health Organization, Guidelines for drinking-water quality [electronic resource]:

incorporating first addendum. Vol. 1, Recommendations, Third ed., 2006.

8. Simis, S.G.H., S.W.M. Peters, and Gons, H. J., “Remote sensing of the cyanobacterial pigment 

phycocyanin in turbid inland water,” Limnol. Oceanogr., Vol. 50, No. 1, 2005, pp. 237–245.

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13. SUPPLEMENTARY NOTES

14. ABSTRACT

Hyperspectral imagers have significant capability for detecting and classifying waterborne constituents. One particularly appropriate 

application of such instruments in the Great Lakes is to detect and monitor the development of potentially Harmful Algal Blooms (HABs). 

Two generations of small hyperspectral imagers have been built and tested for aircraft based monitoring of harmful algal blooms. In this 

paper a discussion of the two instruments as well as field studies conducted using these instruments will be presented. During the second 

field study, in situ reflectance data was obtained from the Research Vessel Lake Guardian in conjunction with reflectance data obtained with 

the hyperspectral imager from overflights of the same locations. A comparison of these two data sets shows that the airborne hyperspectral 

imager closely matches measurements obtained from instruments on the lake surface and thus positively supports its utilization for detecting 

and monitoring HABs. 

15. SUBJECT TERMS

Imaging spectrometers; Remote sensing 

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