7

Prepared in cooperation with the Houlton Band of Maliseet Indians

Evaluation of Aerial Thermal Infrared Remote Sensing to 

Identify Groundwater-Discharge Zones in the 

Meduxnekeag River, Houlton, Maine

Open-File Report 2013–1168

U.S. Department of the Interior

U.S. Geological Survey
THIS PAGE INTENTIONALLY LEFT BLANK
Prepared in cooperation with the Houlton Band of Maliseet Indians

Evaluation of Aerial Thermal Infrared Remote Sensing to 

Identify Groundwater-Discharge Zones in the 

Meduxnekeag River, Houlton, Maine

By Charles W. Culbertson, Thomas G. Huntington, James M. Caldwell, and Cara O’Donnell

Open-File Report 2013–1168

U.S. Department of the Interior

U.S. Geological Survey

i
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2014

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Suggested citation:

Culbertson, C.W., Huntington, T.G., Caldwell, J.M., and O’Donnell, Cara, 2014, Evaluation of aerial thermal 

infrared remote sensing to identify groundwater-discharge zones in the Meduxnekeag River, Houlton, Maine: 

U.S. Geological Survey Open-File Report 2013–1168, 21 p., http://dx.doi.org/10.3133/ofr20131168.

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endorsement by the U.S. Government.

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ISSN 2331-1258 (online)

ii
Acknowledgments

The authors thank Larry Davis, Davis Aviation, Kent, Ohio, for performing the aerial surveys 

and collecting and analyzing the aerial infrared videography. 

iii
Contents

Acknowledgments..........................................................................................................................................................iii

Abstract ......................................................................................................................................................................... 1

Introduction.................................................................................................................................................................... 1

Purpose and Scope ....................................................................................................................................................... 3

Previous Investigations.................................................................................................................................................. 3

Description of Study Area .............................................................................................................................................. 4

Aerial and Ground-Based Methods of Data Collection .................................................................................................. 5

TIR Remote Sensing of Surface-Water Temperature Anomalies............................................................................... 5

Aerial TIR Data Collection ...................................................................................................................................... 5

Mapping and Image Processing ............................................................................................................................. 6

Characterization and Ground Verification of Aerially Identified Thermal Anomalies................................................... 6

Identification of Thermal Anomalies............................................................................................................................... 7

Summary ....................................................................................................................................................................... 7

References Cited........................................................................................................................................................... 7

Figures

Figure 1. Map showing hydrography of the Meduxnekeag River watershed in northeastern Maine. ......................... 12

Figure 2. Map showing locations of USGS streamgages and sampling stations in the Meduxnekeag River 

watershed near Houlton in northeastern Maine. .......................................................................................................... 13

Figure 3. Map showing land use in the Meduxnekeag River watershed near Houlton in northeastern Maine............ 14

Figure 4. Map showing topography and hydrography of the Meduxnekeag River watershed near Houlton in 

northeastern Maine...................................................................................................................................................... 15

Figure 5. Map showing surveillance reaches along the Meduxnekeag River near Houlton, Maine, in the aerial 

thermal-imaging study on A, December 3–4, 2003, and B, November 26, 2004. ........................................................ 16

Figure 6. Images of thermal anomalies for discharges into the Meduxnekeag River near Houlton, Maine, during 

the A, December 3–4, 2003, flight and the B, November 26, 2004, flight. ................................................................... 17

Tables

Table 1. Thermal anomalies identified in the Meduxnekeag River near Houlton, Maine, during a flight on 

December 3 from 23:45 to 4:30 Eastern Standard Time on December 4, 2003. ..................................................... 20

Table 2. Thermal anomalies identified in the Meduxnekeag River near Houlton, Maine, during a flight on 

November 26, 2004, from 19:14 to 23:02 Eastern Standard Time........................................................................... 21

iv
Conversion Factors, Datum, and Abbreviations

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2)

acre 0.004047 square kilometer (km2)

square foot (ft2) 0.09290 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2)

Flow rate

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

cubic foot per second (ft3/s) 28.32 liter per second (L/s)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C=(°F–32)/1.8

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.

Wavelengths of thermal radiation bands are measured in micrometers (μm).

The resistance of the thermal imager is given in ohms (Ω).

Abbreviations

AIDIA aerial infrared digital imaging analysis

DDT dichloro-diphenyl-trichloroethane

DEP Department of Environmental Protection

GPS global positioning system

HBMI Houlton Band of Maliseet Indians

TIR thermal infrared

USGS U.S. Geological Survey

VED video encoder-decoder

v
Evaluation of Aerial Thermal Infrared Remote Sensing to 

Identify Groundwater-Discharge Zones in the 

Meduxnekeag River, Houlton, Maine

By Charles W. Culbertson1, Thomas G. Huntington1, James M. Caldwell1, and Cara O’Donnell2 

Abstract

Residents of the area near Houlton, Maine, have observed seasonal episodic blooms of algae and 

documented elevated concentrations of fecal-coliform bacteria and inorganic nutrients and low 

dissolved oxygen concentrations in the Meduxnekeag River. Although point and nonpoint sources of 

urban and agricultural runoff likely contribute to water-quality impairment, the role of shallow 

groundwater inflows in delivering such contaminants to the Meduxnekeag River has not been 

well understood. 

To provide information about possible groundwater inflows to the river, airborne thermal 

infrared videography was evaluated as a means to identify and classify thermal anomalies in a 25-mile 

reach of the mainstem and tributaries of the Meduxnekeag River near Houlton, Maine. The U.S. 

Geological Survey, in cooperation with the Houlton Band of Maliseet Indians, collected thermal 

infrared images from a single-engine, fixed-wing aircraft during flights on December 3–4, 2003, and 

November 26, 2004. 

Eleven thermal anomalies were identified on the basis of data from the December 2003 flight 

and 17 from the November 2004 flight, which covered the same reaches of stream. Following image 

analysis, characterization, and prioritization, the georeferenced infrared images of the thermal anomalies 

were compared to features on topographic maps of the study area. The mapped anomalies were used to 

direct observations on the ground to confirm discharge locations and types of inflow. The variations in 

grayscale patterns on the images were thus confirmed as representing shallow groundwater-discharge 

zones (seeps), outfalls of treated wastewater, or ditches draining runoff from impervious surfaces.

Introduction

Groundwater discharge from shallow aquifers to surface waters represents a substantial 

environmental component of the flow in most rivers and streams, accounting for as much as 50 percent 

of average annual streamflow (Winter and others, 1998). Additionally, this discharge is important for 

maintaining stream base flow and temperature stability during summer dry periods, thereby sustaining 

critical habitat for native flora and fauna (Winter and others, 1998; Torgersen and others, 1999; Hayashi 

and Rosenberry, 2002). 

Groundwater discharge to streams and rivers varies broadly over spatial and temporal scales as a 

function of geologic and hydrologic setting (Sear and others, 1999). Discharge can occur as diffuse 

1

U.S. Geological Survey.

2

Houlton Band of Maliseet Indians, Natural Resources Staff, Maine.

1

 
(nonpoint-source) flow or focused (point-source) flow depending on variables such as bedrock and 

sediment morphology, hydraulic conductivity of the sediment layers and plant communities, streambed 

topography and permeability, hydraulic gradients driven by precipitation and snowmelt, and stream 

stage (Fan and others, 2007; Winter and others, 1998; Alley and others, 2002; Harvey and Bencala, 

1993; Rosenberry and others, 2000; Conant, 2004; Sear and others, 1999). Groundwater discharge may 

also be a significant vector for urban- and agricultural-contaminant inputs to surface-water systems 

(Focazio and others, 1998; Fryar and others, 2000). Contaminant loads delivered to surface waters 

through groundwater pathways can be a substantial proportion of the total annual load (Taniguchi and 

others, 1997; Focazio and others, 1998). In a study of the Chesapeake Bay watershed, groundwater 

nitrate load contributed about half of the total annual nitrogen load to streams in the watershed 

(Bachman and others, 1998). In addition to geologic setting, the nature and magnitude of these 

contaminant loads are affected by land use and daily-to-seasonal fluctuations in the hydrologic regime 

within a particular watershed (Hayashi and Rosenberry, 2002; Fryar and others, 2000; Wroblicky and 

others, 1998). 

Conventional methods that use instream data recordings of temperature and specific conductance

to detect the source of groundwater provide information that is temporally continuous but constrained to 

reaches generally less than a kilometer long, with many potential discharge zones remaining undetected 

(Lowry and others, 2007; Torgersen and others, 2001). Other methods for characterizing groundwater 

discharge to surface waters have been employed, including seepage-meter measurements (Lee, 1977; 

Murdoch and Kelly, 2003; Paulsen and others, 2001; Rosenberry and Morin, 2004), piezometric 

measurements (Lee and Cherry, 1979; Winter and others, 1988; Kelly and Murdoch, 2003), temperature 

surveys (Lowry and others, 2007; Anderson, 2005; Conant, 2004; Constanz and Stonestrom, 2003; 

Constanz, 1998), studies with dyes and conservative tracers (Flury and Wai, 2003; Harvey and Bencala, 

1993; Lee and others, 1980), and the assessment and modeling of hydrogeochemical data (Fryar and 

others, 2000; Harvey and Wagner, 2000; Harbaugh, 2005). 

Thermal infrared (TIR) remote sensing has been used to measure surface-water temperatures and 

circulation patterns in larger water bodies such as lakes (Anderson and others, 1995; Kay and others, 

2005), measure sea-surface temperatures (Donlon and others, 2002), assess reach- and watershed-scale 

stream-temperature patterns (Atwell and others, 1971; Faux and others, 2001; Kay and others, 2001; 

Torgersen and others, 2001), identify important habitat-sustaining thermal refugia for fish in streams 

(Belknap and Naiman, 1998; Torgersen and others, 1999), and identify zones of groundwater discharge 

into rivers, streams and estuaries (Banks and others, 1996; Urish and Gomez, 2004; Loheide and 

Gorelick, 2006). Aerial TIR remote sensing has been used successfully in studies in the northeastern 

U.S. and elsewhere to identify zones of groundwater discharge into surface waters (Roseen and others, 

2002; Ballestero and Roseen, 2003; Urish and Gomez, 2004; Mulligan and Charette, 2006; Loheide and 

Gorelick, 2006; Banks and others, 1996; Torgersen and others, 2001; Raabe and Bialkowska-Jelinska, 

2010).

Aerial TIR remote-sensing technology is particularly useful in that it provides a spatial context 

for evaluating relationships between land use and water quality in a watershed (Torgersen and others, 

2001). Surface temperatures over long river reaches are easily surveyed at high resolution, and single 

images can be related to large areas of a water body. TIR sensors are capable of resolving temperature 

anomalies as small as 0.08 °C at resolutions of less than 1 meter (m) in surface waters; however, they 

cannot penetrate the water column below the upper 0.1 millimeter (mm) of the water surface (Torgersen 

and others, 2001; Kay and others, 2005). The detection of thermal anomalies in a water body is possible 

because of surficial thermal-energy variations caused by disruptions in the normal (in-situ) thermal flow 

in the stream. TIR imaging of potential groundwater-discharge zones relies on groundwater 

2
temperatures, which are thermally stable compared to seasonally variable surface-water temperatures 

(Banks and others, 1996). TIR imagery is typically displayed as grayscale with shades of gray 

representing differences in surface temperature. Generally, lighter shades of gray in IR images indicate

warmer water, and darker gray cooler water (Banks and others, 1996; Torgersen and others, 2001; 

Whited and others, 2002).

Although point and nonpoint sources of urban and agricultural runoff likely contribute to waterquality impairment, the role of groundwater in delivering these contaminants to the Meduxnekeag River

is not well understood. In December 2003 and November 2004, the U.S. Geological Survey (USGS), in 

cooperation with the Natural Resources Department of the Houlton Band of Maliseet Indians (HBMI), 

used aerial TIR videography as a means to identify and map spatial distributions of thermal anomalies 

along a 25-mile (mi) reach of the mainstem and tributaries of the Meduxnekeag River, near Houlton, 

Maine (fig. 1). Thermal anomalies were characterized and ranked on the basis of grayscale tonal 

intensities on the TIR images and the locations of the anomalies relative to the main-stem of the river. 

Aerially imaged thermal anomalies that were evaluated as being potentially significant discharges to the 

river were confirmed by ground verification; however, this verification did not include in situ 

measurements of water-surface temperatures.

Purpose and Scope

This report presents information on the use of aerial TIR sensing to identify potential 

groundwater and other thermal discharge zones on a 25-mi reach of the Meduxnekeag River near 

Houlton, Maine. The report evaluates the viability of the use of TIR remote sensing as a technique to

identify and map potential groundwater seeps and other inflows, such as flows from natural springs,

storm drains, or discharge pipes associated with urban activities along the Meduxnekeag River;

characterizes the potential importance of discharges to the river identified by aerially imaged thermal 

anomalies; and describes the process of ground confirmation of thermal anomalies identified on TIR 

imagery as those of potential importance.

Previous Investigations

The Houlton Band of Maliseet Indians, Department of Natural Resources, has actively 

monitored the water quality of the river and its tributaries for more than two decades, observed seasonal 

episodic blooms of nuisance filamentous algae, and documented elevated concentrations of fecalcoliform bacteria and inorganic nutrients as well as low dissolved oxygen concentrations (unpublished 

data on file with the HBMI). 

Several organizations have previously documented water-quality problems in the Meduxnekeag 

River. The Maine Department of Environmental Protection (DEP) sampled for total phosphorus and 

other indicators of stream water-quality and identified point sources that could be contributing to 

impairment of the river (Maine Department of Environmental Protection, 2000). Independent 

investigators found that algal mats covered as much as 90 percent of the streambed during the summer 

at the sites they monitored (William Ball, Acheron Engineering, Environmental and Geologic 

Consultants, written commun., 2001). Fish-consumption advisories have been issued for the 

Meduxnekeag River because of elevated levels above Maine DEP standards of the pesticide dichlorodiphenyl-trichloroethane (DDT) in fish tissue (Maine Department of Environmental Protection, 2002) 

and for all Maine rivers because of elevated levels of mercury in fish tissue (Maine Department of 

Environmental Protection, 1998b). The river’s water quality is affected by sediments and pesticides in 

agricultural runoff, stormwater runoff and sewer overflow from urban commercial and residential areas,

3
inflows from rural residential septic systems, and wastewater and thermal effects from industrial areas. 

Schalk and Tornes (2005) suggested that sediment, nutrients, and organic compounds from agricultural, 

urban, and industrial areas are likely mobilized during high seasonal periods of runoff.

Description of Study Area

The Meduxnekeag River in southeastern Aroostook County in northern Maine drains 516 square 

miles (mi2

) (fig. 1) at its confluence with the St. John River in New Brunswick, Canada. The river 

begins at Meduxnekeag Lake, 8 mi west of the town of Houlton, Maine. The South Branch joins the 

Meduxnekeag River near Houlton where the river turns north-northeast, flowing for approximately 

10 mi before it crosses the Canadian border to its confluence with the St. John River. Near Houlton, 

Maine, at the most downstream point where streamflow is measured by the USGS (station 

ID 01018035), the drainage area is 257 mi2 (fig. 2). Upstream from the Canadian border, the 

Meduxnekeag River has a drainage area of 289 mi2 (Fontaine and others, 1982). The watershed includes

67 mi of the main-stem river and 290 mi of tributaries. Many small lakes in the upstream parts of the 

watershed are at a higher elevation than the agricultural lands in the lower part of the watershed.

Northeastern Maine is characterized by cold winters and short, warm summers. The growing 

season is 100 to 125 days. Average annual precipitation is about 39 inches (in.), which includes the 

water equivalent of 95 in. of snow. Average temperatures range from 12 °F in January to 68 °F in July

(National Oceanic and Atmospheric Administration, 2002). Although precipitation is distributed fairly 

evenly throughout the year, most of the annual streamflow occurs during the spring snowmelt period 

and before evapotranspiration increases following leafout. Snowmelt runoff has been observed to cause 

severe erosion in late winter and early spring (Southern Aroostook County Soil and Water Conservation 

District, 1993). Occasional large summer and fall storms can also result in substantial amounts 

of runoff. 

The USGS maintains three streamflow gages (or streamgages) in the study area (fig. 2). 

Streamgage 01017960, the most upstream streamgage, was established in 2003 in cooperation with the 

Maine DEP, Town of Houlton, and Tate and Lyle Manufacturing above the confluence of the main stem 

of the Meduxnekeag River and the South Branch. This streamgage is about 2 mi upstream from the 

town of Houlton, and the watersheds of its major tributaries Mill Stream and Mill Brook are primarily 

forested (figs. 1, 3). Long-term streamflow statistics for this streamgage were not calculated for this 

upstream site because of the short period of record.

Station 01018000, Meduxnekeag River near Houlton, was active from 1940 to 1982. During this

time period, rating curves were established, and periodic measurements of water temperature, specific 

conductance, and streamflow were made. Station 01018000 was reactivated in 2003, in cooperation with 

HBMI, for additional streamflow measurements and water-quality monitoring. Of 56 measurements of 

streamflow on record for station 01018000, 35 were made during the spring months March to May; the

median for these measurements was 1,760 cubic feet per second (ft3

/s). Median measured streamflow 

during the rest of the year was 101 ft3/s. The peak recorded flow at station 01018000 was 6,010 ft3/s on 

April 4, 1976, probably in response to snowmelt runoff. Station 01018035, Meduxnekeag River at

Lowery Road near Houlton, Maine, the most downstream main-stem station on the Meduxnekeag River, 

was established in July 2005, in cooperation with HBMI, for additional streamflow measurements and 

water-quality monitoring.

One town (Houlton, population 5,270 in 2000) and one industry, a manufacturing plant, have 

permitted outfalls to the Meduxnekeag River (Maine Department of Environmental Protection, 1998a, 

2003). Houlton’s municipal wastewater outfall is just downstream from the town limits. The 

manufacturing plant, which processes food starch (Town of Houlton, 2004), is just downstream from 

4
station 01017960 and upstream from the confluence of the South Branch with the main stem of the 

Meduxnekeag River. Most irrigation of agricultural fields is by withdrawals from the Meduxnekeag 

River (Matthew Williams, University of Maine Extension, written commun., 2004). The demand for 

irrigation water, however, puts stress on aquatic habitat during low-flow periods (Aroostook Water and 

Soil Management Board, 1996). 

Land cover in the Meduxnekeag River watershed is primarily forest with smaller amounts of

agriculture (fig. 3). Forests cover about 79 percent of the watershed; agricultural lands, about 

17 percent; and urban areas and open water, about 4 percent (Southern Aroostook County Soil and 

Water Conservation District, 1993). In 1993, agricultural lands included approximately 23,900 acres of

active cropland, 3,900 acres of hay and pasture, and 3,000 acres of grassland. Some 393 farms of all 

sizes with 2,443 separate fields occupy 30,800 acres of agricultural land. About 20,000 acres of 

potatoes, most commonly in rotation with grain, are grown on 212 farms. Fifty-two livestock operations 

support 2,350 animals, mostly dairy or beef cattle. Most of the agricultural land is concentrated in the 

lower half of the watershed in and downstream of the Houlton area. The general trend in land use is 

toward gradual increases in urban and suburban areas at the expense of agricultural and forested land 

(Southern Aroostook County Soil and Water Conservation District, 1993).

The thickness of unconsolidated deposits in the Meduxnekeag River watershed is variable. 

In general, the overburden is calcareous till derived from weathered bedrock (Thompson and Borns, 

1985). Much of the soil is classified as highly erodible or potentially highly erodible (Arno, 1964;

U.S. Department of Agriculture, 1994). Most of the arable soils are in agricultural production, and the

steep, stony, and poorly drained soils are in forests (Arno, 1964). Land surface is rolling, with hills 

reaching an elevation of 200 to 500 feet (ft) above valley floors (fig. 4). 

Aerial and Ground-Based Methods of Data Collection

Aerial TIR images for this study were collected from a single-engine, fixed-wing aircraft on 

December 3–4, 2003, and November 26, 2004. With the images obtained during the two flights, surfacewater thermal anomalies were interpreted as shallow groundwater-discharge zones (seeps), outfalls of 

treated wastewater, or ditches draining runoff from impervious surfaces.

TIR Remote Sensing of Surface-Water Temperature Anomalies

Groundwater discharge zones (seeps), natural springs, and surface drains in the study area were 

identified as thermal anomalies by using aerial TIR remote sensing (provided by Davis Aviation, Kent, 

Ohio). Thermal anomalies were assessed on two separate occasions: December 3–4, 2003, between 

23:45 and 04:30 Eastern Standard Time (EST); and November 26, 2004, between 19:14 and 23:02 EST. 

These dates were chosen to target seasonal low-flow periods and low infrared and visual interferences 

caused by tree foliage and to capture maximum temperature gradients between groundwater and other 

inputs relative to the in situ surface-water temperature of the river. Because the surveillance was done 

when stream temperatures were close to freezing, shallow groundwater-seepage zones or inputs from 

other sources such as natural springs, pipes, drains, and septic systems associated with thermal 

anomalies were expected to be warmer than the receiving river water.

Aerial TIR Data Collection

TIR images were made by a Mitsubishi IR–M600 Thermal Imaging Camera (Mitsubishi, Tokyo, 

Japan) equipped with a platinum silicide Schottky-Barrier infrared detector and a polarized infrared

50-mm f/1.2 lens. The detectable thermal-radiation wavelength band for the detector was 3–5 μm. The 

5
resolution of the camera was 512 by 512 pixels, and it provided a sensitivity of 0.08 °C and a field 

recording speed of 60 frames per second. The angular field of view of the detector equipped with the 

50-mm lens was 14° (horizontal) by 11° (vertical). From an altitude of 500 m, the field of view on the 

ground equated to approximately 135 m (horizontal) by 105 m (vertical). The TIR camera was mounted 

in a single-engine fixed-wing aircraft above an opening in the floor of the fuselage, enabling a straightdown orientation. Imaging altitudes ranged from 500 to 800 m above ground surface. Flight paths for 

both aerial assessments began at Meduxnekeag Lake, headwater for the Meduxnekeag River, and 

continued approximately 25 river miles downstream through the town of Houlton to the Canadian 

border. Aerial surveillance also covered tributaries near their confluence with the river’s main stem, as 

well as sections of the South Branch from Cary to Carys Mill and the North Branch from the Canadian

border to approximately the river’s confluence with Meadow Brook.

Mapping and Image Processing

Real-time infrared images were displayed to the pilot on a video monitor and simultaneously 

recorded by a Sony DCR–TRV900 digital video recorder (Sony, Tokyo, Japan). The video output of the

thermal imager (RS170, 75 ohms) was routed through a video encoder-decoder (VED) that labeled the 

video with a continuous stream of global positioning system (GPS)-derived information, including date, 

time, latitude, longitude, altitude, and air speed. GPS locations were obtained each second and used to 

georeference frames on the video tape. A bar code containing the same alphanumeric GPS information 

appeared on the left side of the infrared images and was used by the VED during video playback and 

analysis. The aerial infrared digital-imaging analysis (AIDIA) included the use of 8.5-by-11-inch map 

sheets from DeLorme’s MapExpert 2.0, annotated USGS 7.5-minute topographic maps, original 

MiniDV digital videotape of infrared imagery, and CD–ROMs with images of the thermal anomalies 

identified during each of the flights. Although aerial TIR imaging can provide accurate measurements of 

surface-water temperatures, actual surface-water temperature data were not acquired for this study. 

Instead, identified thermal anomalies were mapped by using tonal differences in grayscale on the digital 

IR video images. Because of the seasonal timing of the flight, surface-water temperatures were assumed 

to be lower than the groundwater temperatures. The thermal anomalies appear as areas of brighter 

contrast on the image.

Characterization and Ground Verification of Aerially Identified Thermal Anomalies

Surface-water temperatures of the Meduxnekeag River vary seasonally and are very cold 

(4–6 °C) during late fall and early winter compared to warmer, more thermally stable (10–12 °C) 

groundwater. Warmer water discharges appear as points that are lighter or brighter on the TIR images 

than the darker (colder) receiving river water. Images were evaluated on the basis of grayscale tonal 

contrast of the thermal anomaly; higher contrast was generally interpreted as representing a greater 

temperature difference between the discharge and the receiving river water. On the basis of a qualitative 

assessment of grayscale contrast, thermal anomalies identified in the TIR images were assigned a 

preliminary characterization as groundwater seeps, discharges from surface drains or pipes, or another 

type of warm water input (tables 1 and 2). Thermal anomalies were then prioritized for ground 

verification on the basis of the intensity of grayscale contrast (a function of temperature, volume, and 

velocity of discharge), preliminary characterization, and proximity to the Meduxnekeag River. 

Following image analysis, characterization, and prioritization, the georeferenced infrared images of the 

thermal anomalies were compared to features on topographic maps of the study area to direct 

observations on the ground to confirm discharge location and type.

6
Identification of Thermal Anomalies

Eleven thermal anomalies were identified on the basis of data from the December 2003 flight 

(fig. 5, table 1), and 17 were identified on the basis of data from the November 2004 flight (fig. 5 (some 

not shown to allow larger map scale), table 2). Temperature anomalies were caused by the discharge of 

groundwater (including shallow groundwater) or surface water from drains, ditches, or wastewater 

outfalls into colder river water. The types of anomalies identified in this study included groundwater 

seeps, outfalls from surface drains or ditches originating from buildings, and permitted discharge from 

outfall of the Houlton wastewater-treatment plant. Groundwater seeps were identified on the banks of 

small tributary streams, the Meduxnekeag River mainstem, near Nickerson Lake adjacent to the river, in 

streambeds and flood plains adjacent to the river, and on a hillside. TIR images of most of the identified 

thermal anomalies are shown on figures 6A and B. The seeps appear as bright areas against 

backgrounds in various shades of gray. Thermal anomaly no. 17 observed during the November 2004 

flight was identified as a seep originating near a farm and possibly connected to the Meduxnekeag River 

(figs. 5 and 6B, table 2). The wide variation in the shape, size, and intensity (brightness contrast) of the 

temperature anomalies may indicate a range of different seep or surface-drain discharge rates and 

different rates of mixing with surface water.

Summary

Aerial thermal infrared remote-sensing surveys were conducted by the U.S. Geological Survey, 

in cooperation with the Natural Resources Department of the Houlton Band of Maliseet Indians, during 

aircraft flights over a 25-mile reach of the mainstem of the Meduxnekeag River near Houlton, Maine, on 

December 3–4, 2003, and November 26, 2004. Eleven thermal anomalies were identified on the basis of 

data from the December 2003 flight, and 17 were identified on the basis of data from the November 

2004 flight. Analyses of thermal infrared images indicated groundwater-discharge zones, as well as 

other types of thermal inputs, including outfalls from surface drains or ditches originating from 

buildings and permitted discharge from the outfall of the Houlton Wastewater Treatment Plant. All of 

the thermal anomalies were found to be contributing sources of inflow. The use of aerial thermal 

infrared remote-sensing was instrumental in locating these seeps.

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11
12

Figure 1. Map showing hydrography of the Meduxnekeag River watershed in northeastern Maine. Colors are 

used only to differentiate individual subbasins.
13

Figure 2. Map showing locations of USGS streamgages and sampling stations in the Meduxnekeag River 

watershed near Houlton in northeastern Maine.
14

Figure 3. Map showing land use in the Meduxnekeag River watershed near Houlton in northeastern Maine.
15

Figure 4. Map showing topography and hydrography of the Meduxnekeag River watershed near Houlton in 

northeastern Maine.
16

Figure 5. Map showing surveillance reaches along the Meduxnekeag River near Houlton, Maine, in the aerial 

thermal-imaging study on A, December 3–4, 2003, and B, November 26, 2004.
17

Figure 6. Images of thermal anomalies for discharges into the Meduxnekeag River near Houlton, Maine, during 

the A, December 3–4, 2003, flight (images 61–72) and the B, November 26, 2004, flight (images 1–18). [Image 

numbers are anomalies described in tables 1 and 2.]
18

Figure 6. Images of thermal anomalies for discharges into the Meduxnekeag River near Houlton, Maine, 

during the A, December 3–4, 2003, flight (images 61–72) and the B, November 26, 2004, flight (images 1–18). 

[Image numbers are anomalies described in tables 1 and 2.]—Continued
19

Figure 6. Images of thermal anomalies for discharges into the Meduxnekeag River near Houlton, Maine, 

during the A, December 3–4, 2003, flight (images 61–72) and the B, November 26, 2004, flight (images 1–18). 

[Image numbers are anomalies described in tables 1 and 2.]—Continued
Table 1. Thermal anomalies identified in the Meduxnekeag River near Houlton, Maine, during a flight on December 3 from 23:45 to 4:30 Eastern 

Standard Time on December 4, 2003.

[Latitude and longitude in degrees, minutes, and seconds (decimal seconds format). The anomalies are classified generally as GS, groundwater seep; WS, 

water seep from the ground at the edge of the water; and other, as noted after the anomaly's number. Each thermal anomaly is qualitatively described based on 

the size and magnitude of the changes in white intensity or brightness observed on the image. Definitions of abbreviations: NW–SE, northwest to southeast; 

NE, northeast; NW, northwest; NE–SW, northeast to southwest; N–S, north to south]

Anomaly 

number Anomaly feature in figure 6 Latitude Longitude Classification of thermal anomaly

61 Bright feature near center of image 46o 05' 55.62"N 68o 00' 30.60"W GS or WS on shore of mostly frozen 

Meduxnekeag Lake

62 Bright narrow feature at center of image with NW–SE 

orientation

46o 06' 05.94"N 67o 52' 17.82"W GS or WS at shoreline

63 Bright feature in NE quadrant of image 46o 06' 19.50"N 67o 52' 51.00"W GS or WS at shoreline

65 Bright feature near center of image 46o 07' 31.26"N 67o 50' 13.32"W Storm water drain near building, east

side of bridge

66 Bright feature in NE quadrant of image, partially obscured by 

bridge

46o 07' 33.90"N 67o 50' 29.94"W Storm water drain near building, west 

side of bridge

67 Long narrow, curved feature near center of image 46o 07' 48.60"N 67o 50' 09.96"W Drainage, possibly from intermittent or 

small creek

68 Narrow features at left center of image 46o 08' 02.28"N 67o 49' 52.26"W GS from hillside

69 Bright feature at right center of image 46o 08' 07.38"N 67o 49' 45.54"W Possible GS or creek outlet to river

70 Bright features near center of image 46o 08' 24.00"N 67o 49' 21.30"W GS

71 Narrow feature in NW quadrant of image with NE–SW 

orientation; also in NE quadrant of image with N–S orientation

46o 08' 46.50"N 67o 49' 29.04"W Discharge from wastewater-treatment 

plant

72 Bright features at center and NE quadrant of image; long 

narrow, curved feature at lower center to SE quadrant of image

46o 11' 53.04"N 67o 48' 12.18"W GS; warm flowing surface water

20
Table 2. Thermal anomalies identified in the Meduxnekeag River near Houlton, Maine, during a flight on November 26, 2004, from 19:14 to 23:02 

Eastern Standard Time.

[Latitude and longitude in degrees, minutes, and seconds (decimal seconds format). The anomalies are classified generally as GS, groundwater seep; WS, water 

seep from the ground at the edge of the water; and other, as noted after the anomaly's number. Each thermal anomaly was qualitatively described based on the size 

and magnitude of the changes in white intensity or brightness observed on the image. Definitions of abbreviations: SW–NE, southwest to northeast; NW, 

northwest; NW–SE, northwest to southeast; E–W, east to west]

Anomaly 

number Anomaly feature in figure 6 Latitude Longitude Classification of thermal anomaly

1 Bright features at center and NW quadrant of image 46o 07' 37.00"N 67o 50' 34.04"W Two drains from buildings (65 and 66 in table 1)

2 Bright feature near center of image 46o 07' 59.97"N 67o 50' 48.08"W GS/creek—warm

3 Bright features at upper center and left center of image 46o 08' 05.65"N 67o 50' 54.25"W GS at tributary

4 Bright features at center and upper center of image 46o 07' 46.85"N 67o 50' 50.45"W GS at bank

5 Narrow bright features at center of image 46o 07' 56.04"N 67o 50' 48.08"W GS

6 Bright feature at center of image 46o 08' 51.42"N 67o 51' 12.61"W GS

7 Narrow features near center (SW–NE orientation) and 

NW quadrant of image

46o 08' 53.23"N 67o 49' 33.15"W Discharge from wastewater-treatment plant (71 in 

table 1)

8 Narrow faint white feature in the NW quadrant to 

upper center of image

46o 17' 07.52"N 67o 47' 01.42"W Creek with groundwater warmth

9 Bright features near center of image 46o 17' 39.16"N 67o 47' 07.94"W GS—minimum flow

11 Bright features near center and upper center of image 46o 18' 21.28"N 67o 49' 47.90"W GS at bank

12 Bright feature at upper center of image (SW–NE 

orientation)

46o 18' 28.14"N 67o 52' 00.53"W GS

13 Bright feature at right center of image 46o 18' 52.34"N 67o 52' 24.20"W Small GS

14 Bright feature at left center of image 46o 18' 53.28"N 67o 54' 29.75"W GS in small creek on Meduxnekeag River

15 Faint narrow features near center of image having 

slight NW–SE orientation

46o 07' 09.14"N 67o 51' 21.42"W Warm-water seeps from small pond adjacent to 

Meduxnekeag River

16 Bright feature at center of image 46o 06' 19.89"N 67o 52' 52.21"W GS at bank (same feature as 63 in table 1)

17 Narrow bright feature with slight E–W orientation and 

bright spot at center of image

46o 06' 01.73"N 67o 53' 50.27"W Small creek discharge and GS near farm

18 Bright features at center to right center of image (other 

bright spot is exhaust from a vehicle)

46o 05' 58.86"N 67o 56' 22.05"W Unknown warm-water source near house on lake

21
Prepared by the Pembroke Publishing Service Center.

For more information concerning this report, contact:

Office Chief

U.S. Geological Survey

New England Water Science Center

Maine Office

196 Whitten Road

Augusta, ME 04330

dc_me@usgs.gov

or visit our Web site at:

http://me.water.usgs.gov
ISSN 2331

-1258 (online)

http://dx.doi.org/10.3133/ofr20131168

Culbertson and others—Evaluation of Aerial Thermal Infrared Remote Sensing to Identify Groundwater-Discharge Zones in the Meduxnekeag River—Open-File Report 2013–1168