~I
REMOTE SENSING OF HAWAIIAN COASTAL SPRINGS
USING MULTISPECTRAL AND INFRARED TECHNIQUES
by
Larry K. Lepley
Leonard A. Palmer
Technical Report No. 18
August 1967
No.5 of 5 Reports in Completion
of
GEOPHYSICAL EXPLORATION FOR HAWAIIAN GROUNDWATER, PHASE I
OWRR Project No. B-005-HI, Grant Agreement No. 14-01-0001-1011
Principal Investigators: Doak C. Cox, William M. Adams, Leonard A. Palmer
Project Period: July 1, 1966 to June 30, 1967
The programs and activities described he rein were supported i n par t by fundsprovi ded by the United States Department of the I nt er i or as aut hor i ze d undert he Water Resources Act of 1964, Public Law 88-379 .
Ii
ABSTRACT
Two remote sens~ng techniques of measuring offshore ground-water
spring discharge that have bee n studied are : (iJ mul tispect ral photo
graphy~ and (iiJ infrared thermometry .
During the summer of 1 96 7~ expos ure factors f or filter-film
camera combinations extending outside the visible spectra were experi
mentally determined and tabulat ed . One spectral series of simulated
aer ial photography was obtained . Darkroom procedures and equipment
for multispectral enhancement of the sus pect ed col or di f f erence s
between sea water and offshore spring water in these photographs have
not yet been precisely de fi ned .
Helicop ter f l i ght s with an infrared thermometer have demonstrated
that offshore spr ings can be i dentified by their temperatures . Due
t o t he irregu lar shape ~ size~ and location of these fres h wate r out
flows~ a synoptic t echnique is needed . An infrared scanner i s desira
ble but the present costs ar e prohibitive .
i ii
CONTENTS
LIST OF TABLES •.••• ••.•...••.• ••.•.••.• ••••••••..••.••••..••••••••••vi
LIST OF FIGURES ..••••••••.•.••.•••••••. •.•.•••..•••••.••••••••••••••vi
INTRODUCTION •...•• . ••.....•.••.•.•••.• ; •• •.•••••.•••. •••••••••••.•••. 1
MULTISPECTRAL PHOTOGRAPHY
OBJECTIVE •...•.••.....••.•...•....•...••••.•.•.•.•••.••.••.••.••••••• 7
APPLICATIONS OF MULTISPECTRAL PHOTOGRAPHY •••.•.••••.•..•••••••••••••• 7
INSTRUMENTATION AND FIELD EXPERIMENTS ••••••.••••.••..•..•••••• •••• ••• 8
SUMMARY AND CONCLUSIONS 11
INFRARED THERMOMETRY
OBJECTIVES •••.•.••••.•••••..••••..•.•••••••.•••••••••••.••.••••••• ••17
PRELIMINARY COASTAL SPRING EXAMINATIONS • ••••••••••••• •.•••••••••.•••17
INSTRUMENTATION .••..•• •.••.•• ••••••..•.•.••.••••••••• ••••••..•.•••..19
Laboratory Testing of Instrument Response 21Field Application of Infrared Thermometer 26Temperature Data Recording ~ 29
FIELD TESTING ••.••• •• •••.•••.••••• •• •••••••.••.•••••.••••• •..•.•••••.29
Electric Power and Helicopter Platform 29
RESULTS AND ANALYSIS OF PRELIMINARY FIELD FLIGHTS •.••..•••••••••••••29
SUMMARY AND CONCLUSIONS • • . . . . • . . • • . • • • • ; ••••• ••••. ; ••••••.•••..•••••36
ACKNOWLEDGEMENT ••••••••••.•.••.•.•.•.•.....•••••.••••••••..•••••••.•36
BIBLIOGRAPHY •••.••.••••.•••••••••.• ••••••••••••••••.•••.••••••. ••••• 37
v
LIST OF TABLES
Table1 Filtered ASA Rating: Visible and Ultraviolet Light 102 Filtered ASA Rating: Infrared 103 Contrast in Infrared Image Density and Temperature and
Salinity of Selected Coastal Springs on the Island of Hawaii.19
LIST OF FIGURES
Figure1
2
3
4
5
6
7
8
9
1011
121314
15
16
Spectral Locations of Filters 9Unenhanced Pictures of the Same Scene Photographed; n Different Bands ,. I ,' •••••• • 12
Schematic of Laboratory Enhancement Procedure 13Configuration of Fresh and Salt Water Interface 18A Small Underwater Spring Churning Sand in theShallow Nearshore Waters at Kawai10a Beach, Oahu 20Block Diagram of the Infrared Thermometer. . . . . • . . . . . . . . . . . . . . 22Infrared Passbands in the Transmission of RadientEnergy Through Atmosphere 23Spectral Distribution of Energy for Perfect Emitters 24Laboratory Tests of Repeatability, Response Timeand Accuracy 25
Response Rate of Infrared Thermometer 27Diagram of Operating Velocities and Altitudes for aHe 1i copter ' ' _. . 28
Shock-mounted Instrumentation for Field Testing . •. . . . . . . . . . . .30Flight Path of Preliminary Test F1ights 31Infrared Temperature Profile of Residential andForest Area in Nuuanu Valley 33Infrared Temperature Profile of Sea, Beach, Park,and Urban Areas -' 34
Correlation of the Terrain to Infrared TemperatureProf; 1e 35
vi
INTRODUCTION
Ground-water springs near the shoreline of the Hawaiian Islands
discharge a large unmeasured port ion of the Ghyben-Herzberg fresh-water
lens. Irregular distribution and size of openings in the volcanic rock
through which most Hawaiian ground water flows make accurate flow mea
surements difficult. There are no established methods for studying
coastal springs. Although they have been recognized in the Mediterra
nean since before the time of Christ, and were also known to the ancient
Hawaiians, there is almost no scientific literature about them (Kohout,
1966).
In this project, spectral photography and infrared thermometry
are being evaluated as sensors to develop inexpensive and reliable
methods of detecting and measuring Hawaiian coastal ground-water springs.
These techniques show promise of being useful to coastal ground-water
spring detection.
Photography and photogrammetry has been used for documentation
of hydrologic projects for some time. A relatively new technique uses
multiple photographs in different portions of the light spectrum to
make multiple spectral photographic comparisons of the same objects.
It is possible to recogni ze and differentiate apparently similar ob
jects. The recognition of plant diseases and crop identification as
well as military applications in photo reconaissance and camouflage
detection have made spectral photography valuable (Colwell, 1961; Loh
man and Robinove, 1964).
MULTISPECTRAL PHOTOGRAPHY. Multispectral photography has been care
fully analyzed on various types of ground and plant surfaces but less
experimental data is available on its response to various water sur
faces (Colwell, et aZ., 1966). Spectral photographic experiments to
test multiple passband photography were organized to determine their
usefulness in detection of fresh-water coastal springs. Color filters
were applied to isolate bands of color in photographing the sea surface.
The resulting pictuyes are developed in both positive and negative
transparencies and projected in their various combinations upon a screen
for interpretation. False-color light is used to aid identification
of the effect of each color passband. For example, an obj ect is photo-
2
graphed through blue, green, light-red, and dark-red filters. Both
negative and positive projection transparencies are prepared from each
photograph, providing 8 slides of the object for comparative projection.
A positive black and white transparency photographed through the red
filter, for instance, may be projected onto a screen using any color
of monochromatic light. Other positive arid negative transparencies
photographed through other filters are compared by superposi~g 'them
on the screen in a contrasting monochromatic light. The resulting 'two
color picture on the screen will emphasize only differences between
slides by the dominance of either the false color used or the projec~
tion.
The object is to find a combination which may be useful in en-. : . ' .
hancing color differences that will help to detect an object of interest.
In the present study, a coastal spring may have different organic and
other coloring matter which may be detectable by color enhancement.
INFRARED THERMOMETRY. Infrared thermometry has a clearly defined tech- '
nique of application but a more difficult instrumentation. The theory
of infrared temperature sensing is simple. Gates (1962) described many
of the instruments and their problems. ' Recent development of operational
instrumentation has been stimulated by research directed 't o military
applications of "imaging" radiometers and by research applied to remote
sensing of objects for use in space science applications (Harris and
Woodbridge, 1966). (For a definition of terms imagery and photography~
see Robinove, 1963.)
A military-type imaging radiometer was used by the U. S. Geolo
gical Survey in a study of the temperature distribution of volcanoes
on the island of Hawaii. As an adjunct to those studies, a number of
aerial traverses were made along the coastal areas of the island of
Hawaii. Two hundred nineteen springs were detected by infrared imagery
which registered both warmer and colder temperature anomalies in the
ocean where volcanic warmed and normal ground-water springs occurred
(Fischer, et aZ.~ 1964 and 1966).
The infrared imaging radiometer is well-suited to the detection
and measurement of the relative temperature distributions of coastal
springs, especially in its ability to present a synoptic view of flow
patterns and temperature distribution by registering their location
3
in relation to other known objects. However, imaging radiometers pre
sent difficulties in their inability to give accurate temperature read
ings, their relatively high cost of operation, and the need for highly
skilled technicians to operate the tempermental instruments. They must
be transported in a rather large aircraft capable of supplying the neces
sary power sources and space.
The logistics and cost of infrared imaging are offset by its
efficiency in a cooperative multiple-use program. However, for limited
use to measure small areas or selected areas intermittantly, such as,
documentation of variations with time, the cost is prohibitive. Inex
pensive infrared thermometers which measure the infrared radiant energy
for a small area are available at a more reasonable cost. These instru
ments provide greater accuracy than imaging radiometers but do not pro
vide an instantaneous synoptic view, nor do they provide geographical
orientation to the point of the temperature measurement.
MULTISPECTML PHOTCGMPHYby
LARRY K. LEPLEY
I
7
OBJECTIVE
The objective of the current experiments in multispectral photo
graphy is to devis e a t echnique of enchancing an otherwise imperceptible
color difference, including those in the ultraviolet and infrared wave
bands, for the detection and delineation of coastal spring water bound
aries by their optical differences from the surrounding sea water.
APPLICATIONS OF MULTISPECTRAL PHOTOGRAPHY
Multispectral photography, or multiband spectral reconnaissance,
involves darkroom projection techniques of additive and subtractive
superposition of multiple images of the same scene photographed separately
in color bands between 3000 and 9000 AO. The object of this spectral
separation and opt ical counterbalancing is to produce a brilliant image
in visually contrasting arbitrary colors where natural color contrasts
are visually undetectable (Molineux , 1964).
Studies of human color perception (Land, 1959, Legrande, 1959)
have shown that in the human visual system, combinations of two or
more color bands wi l l produce the s ensation of a third color. For ex
ample, red added to green is perceived as yellow. Optical filters
passing only narrow bands of color cannot be so deceived. This differ
ence between human and instrumental color perception forms the basis for
multispectral color enhancement techniques.
Photographic spectral analysis has been applied to camouflage
detection, agronomy, and forestry (Colwell, 1961, 1965), but only limit
ed data are available on its use on various water surfaces (Ewing, 1965).
Some of the suspected physical differences between spring water
and sea water supporting the search for instrumentally detectable optical
contrasts are:
1) Fresh water contains different dissolved and suspended organic
matter, i .e . ~ tannin dyes from land vegetation in fresh water
as oppose~ to yellow "gelbstoff" from chlorophyl-bearing phyto
plankton in sea water (Kalle ,. 1960);
2) Spectral interference effects from thin organic films on either
water surface may be especially detectable in the near infrared
(visible sea slicks from such films are known to sometimes
8
align themselves with subsurface water structures, such as,
,internal waves);
3) Exsolving gasses bubbling from cold floating spring water warmed
by sea water may throw small droplets of water into the air.
This effervescent mist may be detectable by its scattering of
infrared light (an infrared "fog" layer);
4) Capillary surface waves on the sea water surface may be smoothed
by the spreading surface layer of fresh water. The consequent
modification of surface-reflected skylight caused by the smooth
surface can be enhanced by a comparison of images photographed
through polarizing filters at various orientations.
INSTRUMENTATION AND FIELD EXPERIMENTS
Kahana Bay, Oahu was chosen as the site of field experiments because
it is small, sheltered, and contains submarine springs. The high cliffs
overlooking the bay provide platforms for simulated aerial photography.
A Calumet view camera with wide-angle lens provided the advantages of a
large-size negative, ground-glass viewer, and easily changed components.
The angle of view to the water surface ranges from 8° to 45° from the
horizontal.
The first phase of operations empirically established the filter
factors (the number of times by which the exposure must be increased for
a given filter with a given film) for the filter~film-camera combinations
of more than 20 Wratten filters covering color bands of various widths
ranging from 3000 to 9000 AO. (Figure I shows the spectral locations of
most of these filters.) Films included Polaroid PN and infrared black
and white.
Infrared data were also determined as follows: since there is no '
consistent rating for infrared film used in visible light ,the data recov
ered were based on exposure trials which in most cases go beyond the
the scales normally included on standard ASA light meters. The ASA speeds
listed have therefore been computed from the most useful exposures. Fil
ters selected and factors established are noted in Tables land 2. The
spectral transmissions were determined from Kodak Publication B-3 and
are based on a transmission level of 10%.1
Tables 1 and 2 were compiled by Bruce Erickson.
-ULTRA-VIOLET ·1' VISIBLE UGHT '1- INFRA-RED •
I. PANCHROMATIC FLM (VP)
~JT~ol
~--':'-II I f,-;12B i1 I .rS011 sooo 40 II i:'%11 ' mL 70
L87C _83OOAo 0
o
:~
89 B : d7050 AO ~ u.
..o
LL87 ,ou.7600 AO : ~
o ,
0t-88 A : a7330 AO
L3 4 '(§)
24-
I L 29 -
L 25A -
, 21-
<a>
~_180_llUv_J ~0· ~J L6)~ \I . . . ~(§)
FIGURE 1. SPECTRAL LOCATIONS OF FILTERS.1.0
""'"
10
FI LTEROR
STOP ASA WITHFILTER NO. FILTER COLOR TRANSMISSION RANGE FACTOR I~REASE 50 SPEED FI LM
18 A (W) BLACK PURPLE 3200 AOD_ 3900 AD 400 X 8 2/3 . 125
47 b DARK BLUE 3950 AD - 4700 AD 8 X 3 6. 000
75 DARK BLUE-GREEN 4700 AD - 5050 AD 32 X 5 1. 600
74 DARK GREEN 5200 AD - 5450 AD 20 X 4 1/3 2. 500
21 ORANGE 5200 AD 2 X 25.000
74 + 21 5200 AD - 5450 AD 320 X 8 1/3 .160
11 YELLOW GREEN 4650 AD - 6400 AD 4 X 2 12.000
21 + 11 5200 AD - 6400 AD 10 X 3 1/3 5.000
24 LIGHT RED 5800 AD - 6 X 2 2/ 3 8. 000
11 + 24 5800 AD - 6400 AD 32 X 5 1.600
29 DARK RED 6100 AD 25 X 4 2/3 2. 000
11 + 29 6100 AD - 6400 AD 100 X 6 2/3 . 500
34 DARK VIOLET 3300 AD - 4700 AD & 6500 AD ~ 16 X 4 3. 000
11 + 34 4650 AD - 4700 AD 400 X 8 2/3 . 125
73 DARK YELLOW @ 1% : 5550 AD - 5950 AD !l00 X 8 2/3 .125
72 b DARK ORAI'GE @ 1%: 5900 AD - 6350 AD 500 X 9 .100
TABLE 2. FILTERED ASA RAT ING; INFRARED.
TRANSM ISSIONFILTER NO. RANGE @ 10% ASA AC TUAL EXPOSURE IN SECONDS
89 b FROM 7000 AD ON 10.0000 1 5 @f 36 (ASA 5 OVER WATER )
87 FROM 7600 AD ON 6.000 0 1/ 5 5 @ f 18 IN BRIGHT SUN
87 b FROM 8600 AD ON . 0320 60 5 @ f 22 IN BR IGHT SUN
87 a FROM 9500 AD ON . 0125 60 5 @ f 11 IN BR IGHT SUN
The next phase was the collection of imagery . Instead of using
multiple airborne cameras to obtain simultaneous images through differ
ent filters, the top of the cliff was used as a steady platform to pro
duce sequential imagery of the same s cene wi t h filt er and film changes
between frames. Changes i n the scene due to the fOrward travel of ocean
11
swells were negated by "blurring out" with long time exposures. . Exami
nations of photographs resulting from these initial tests showed that
longer exposures (+ 12 sec) are needed to smooth out water waves and
that a polarizing filter is needed in even the longer wavelengths of
light because the infrared light from foilage on the opposite side of
the bay is reflected from the water surface (Figure 2c).
Figure 2 (a,b,c) shows the initial unenhanced differences in
an image photographed in different bands. Repeat photography and more
surface mapping is needed before the anomalies can be interpreted as
either natural "ground" phenomena or "noise" picked up in the photogra
phic process. To date, only a limited amount of time has been spent on
field and laboratory work in multispectral photography. No enhanced
versions of photographs have yet been produced.
A schematic representation of the laboratory enhancementproce
dure in Figure 3 represents A as two visually indistinguishable color
spots in a "noise" field, and the appearance of the resulting negative
images obtained through any given filters. Posi~ive transparencies,
B, are made from all negatives. A negative transparency from one color
band is then superimposed on a positive transparency from another color
band and visa-versa in C. These composi~es now have enhanced the spot
of one of the respective colors and have cancelled out the background
"noise" field. In D, arbitrarily selected brightly-colored light is
used to project the sandwiched images sequentially and in register upon
the single piece of color film. The resulting image delineates in
brightly contrasting false colors previously subtle color differences
and has "grayed out" areas of original color lying outside of the filter
passbands.
SUMMARY AND CONCLUSIONS
Multispectral photographic equipment has been calibrated for spec
tral sensitivity to sea water. More surface survey is needed before
imagery can be interpreted. Current laboratory work to produce false
color enhanced images will determine feasibility of the technique for
use in locating submarine springs by their optical effects.
('
12
a . Wratten #11 filter (dark green) with polarizer(vertical mode).
b. Wratten #29 filter (visible dark red) with polarizer(vertical mode).
c. Wratten #87b filter (infrared) without polarizer .
FIGURE 2. UNENHANCED PICTURES OF THE SAME SCENE PHOTOGRAPHED IN DIFFERENT BANDS.
A. FIRST STAGE(FIELD WORK)
ORIGINAL SUBJECT
13
FILTERED NEGATIVE NO. I UNFILTERED FILM FILTERED NEGATIVE NO.2
~~~
\0 -7
B. SECOND STAGE(LAB WORK)
\C)
POSITIVE NO. I
C. THIRD STAGE(LAB WORK)
UNFILTERED POSITIVE
7 /~ ~
ARBITRARY COLOR FILTERSONTO ONE PIECE OF COLOR
FILM
/
POSITIVE NO.2
\ - 07
POSITIVE NO.2
COLOR ENHANCED VERSION OFORIGINAL SUBJECT
FIGURE 3. SCHEMATIC OF LABORATORY ENHANCEMENT PROCEDURE.
INFRARED THEPJVUv1ETRYby
LEONARD A, PALMER
17
OBJECTIVES
The infrared thermometry project encompasseQ: (i) study of known
coastal springs to determine approximate size and temperature contrasts,
(ii) laboratory test of instruments and construction of accessory
recording and power equipment, and (iii) aerial traverses to test the
ability of a thermistor bolometer to detect known springs.
PREL IMINARY COASTAL SPRING EXAMINATIONS
Preliminary studies of known areas of coastal springs were con
ducted to establish ground data for later serial traverses . Extensive
traverses in a boat with thermistor temperature and salinity probes of
the Pearl Harbor area (the most promising of spring area of the island of
Oahu) failed to reveal the expected large discharging bodies of fresh
water. The only marked thermal and salinity contrast measured was de
tected adjacent to an electric generating plant cooling water out f a l l.
Most of the springs discharge in swampy areas from which the water flows
in channels to the harbor. It may be that the temperature contrast
between the spring and harbor waters is reduced along the surface fl ow
north .
Efforts were made t o locate large springs on Oahu suitable f or
over-flight traverses with reasonable assurance of thermal contrast .
Various cold-water springs reported by scuba divers and skin divers
were sought and measured from boats and surfboards and with diving
gear. The most promising spring locat ion on Oahu is i n Kahana Bay
on the northshore of Oahu .
A rapid traverse of the coastline of the island of Hawaii was
made to measure the temperature and salinity contrasts of s ome of the
springs detected by Fischer, et aZ . ~ (1966), by infrared imaging aerial
traverses. The typical configuration of t he fresh and salt water in
terface of the coastal springs of the Hawaiian Islands is shown in
Figure 4 . Fresh-water flows from the shoreline or from a spring on
the shallow sea floor. The density of fresh water is l ower than that
of sea water regardless of relative temperatures, theref ore a fresh
water surface layer forms over the more dense sea water. In the mixing
f
WARM SALT WATER
< WARM OR COLDFRESH WATER
FIGURE 4. CONFIGURATION OF FRESH AND SALT WATER INTERFACE. FRESH WATER FLOWS OVER SEA WATER OF GREATER DENSITY.A MIXING ZONE BETWEEN THE FRESH AND SEA WATER SHOWS TURBULENT REFRACTION OF LIGHT AND CAN BE RECOGNIZED BY SKIN DIVERS REGARDLESS OF WATER TEMPERATU~E CONTRASTS.
......00
19
zone between the two bodies of water the turbulent refraction of light
is very pronounced and is a good indication of the presence of fresh
water in the absence of t~mperature contrasts . (Such turbulence is
readily observed by-a diver using a face mask.)
Progressive dispersion away from the spring source occurs by the
mixing and spreading of the fresh water. Not all springs yield high
quality fresh water because mixing occurs within the ground-water body,
but most are at least brackish. The temperature conductivity contrasts
of springs on the island of Hawaii are listed in Table 3.
TABLE 3. CONTRAST IN INFRARED IMAGE DENSITY AND TEMPERATUREAND SALINITY OF SELECTED COASTAL SPRINGS ON THEISLAND OF HAWAI I.
LOCATION IMAGERY DENSITY CONTRASTl TEMPERATURE CONDUCTIVITYSPRING/SEAo F2 SPRING/SEA (mhos)2
REEDS BAY, HILO 0.70 69/76 14,000/40,000
EAST OF HILO 0.66
PUNALUU 1.48 64/75 4000/30,000
PAPA BAY 0.30 NO SPR ING FOUND /40,000(NEAR MILOll I , /76SO. KONA)
lDATA OBTAINED FROM HYDROLOGIC ATLAS HHA-218 , USGS2DATA OBTAINED IN DECEMBER 1966
The largest springs are found near Hilo. However, a large total
discharge probably occurs as dissipated flow along the coasts with uni
form permeability . Many examples of small flows through beach sediments
are reported by swimmers and divers and have been examined as part of
this study, but their measurement has not yet been attempted due to the
difficulty of isolating the ground-water flow from tidal drawdown flow
(Figure 5).
I NSTRUMENTATI ON
Although other thermometers and salinity measuring devices have
been employed, the primary instrument used in this study was a Barnes
Engineering Co. Model IT-3E infrared thermometer. For field surface
studies and laboratory calibration, various mercury thermometers, me
chanical thermometers, and thermistor thermometers have been used. For
salinity measurements an Industrial Instruments (Beckman) model RB3-3341
FIGURE 5. A SMALL UNDERWATER SPRING CHURNING SAND IN THE SHALLOW NEARSHORE WATERS ATKAWAILOA BEACH, OAHU (IN CIRCLE TO LEFT). NUMEROUS SUCH SPRINGS, WHICH CUTSMALL CANALS THROUGH THE SAND, ARE EVIDENT IN THIS AREA (THE NORTHERN BEACHES).PHOTO BY LARRY LEPLEY.
No
21
Conductivity Bridge was used.
The infrared thermometer is essentially a thermistor flake measuring
radiation flux filtered by indium bromide and itron lens to transmit the
7-14 micron passband. The sensing thermistor is chopped by a rotating
blade to produce an AC signal which is verified by a second reference in
an oven within the instrument. Temperature is determined as a difference
between the detecting thermistor and a reference thermistor. (See block
diagram in Figure 6.)
The theory and construction of the infrared thermometer are well
described by Clark and Frank (1963) and Lenschowand Dutton (1964). Sim
ply stated, the radiant flux in the infrared "window" between 7 and 14
microns wavelength is measured (see Figures 7 and S).
Laboratory Testing of Instrument Response
Barnes IT-3E. The infrared thermometer used in this project was labora
tory tested for repeatability of temperature readings, response time,
and temperature accuracy. The instrument is rated to measure temperature
within 1.S oC absolute accuracy and O.SoC resolution. Response time is
specified as 50 milliseconds for 63% rise to true temperature in "fast"
response position and 500 milliseconds in slow response.
The response of the instrument was tested by applying switched
reference temperature targets. The targets with approximately 10°C
difference in temperature were switched on at about 1/2-minute intervals
to produce a square wave temperature reference curve. The results are
shown in Figure 9.
The temperature readings in the fast mode of response fluctuated
2°C continuously with 4° to 5°C noise peaks occurring about 3 per minute
and SoC noise peaks about 1 per minute. Response time was immediate
within the recording instrument capability.
Readings in the slow mode of response were constant within about
1-1/2 0C after approximately 15 seconds log time of instrument to drift.
One second after switching, the instrument recorded about 3° to 4°C error
in temperature reading.
Factory service of the instrument was required shortly after it
arrived. Tests were not made prior to the service. However, the apparent
response on the meter readout was much better before the factory repair.
NN
I IIIIIIIIII I
THERMOSTAT
HEATER
I I I PREAMPLIFIER
,---------IIIIIIIII
'.1
------.., 1-------------,I I II I I
~I I iii m:et~ I !IIII
TO RECORDER I
I , ,:-POST-AMPUFIER ' METER III I AND RECTIFIER
II I/l / '-DETECTOR II I
· 1 OPTICSJ I I BIAS I'I II
BATTERYBOX I
I II II II II SENSING HEAD II ELECTRONICS CONSOLE IL · __~L ~
INCOMINGRADIATION
FIGURE 6. BLOCK DIAGRAM OF THE INFRARED THERMOM~TER (AFTER CLARKE & FRANK, 1963).
- _._- --- - -_._._- - - - - _. .__._ - ---
1.0
0.9
0 .8r-zw 0.7u-~ 0 .6w0 0.5u
z 0.40(J)
0.3(J)-::E(J) 0 .2z<tc:::
0.1r-
00
23
2 3 4 5 6 7 8 9 10 II 12 13 14WAVELENGTH (MICRONS)
FIGURE 7. INFRARED PASSBANDS IN THE TRANSMISSION OF RADIANT ENERGYTHROUGH ATMOSPHERE (AFTER HARRIS AND WOODBRIDGE, 1966). THEINFRARED THERMOMETER MEASURES THE PASSBAND FROM 7 TO 14 MICRONS WAVELENGTH.
24
2018166 8 10 12 14
WAVELENGTH (MICRONS)42o
0.0
0.01
0.10
0.09lJJ0::lJJIa. 0.08en~lJJI
0:: 0.07lJJ _600oKa.z
0.0600::()
~
0:: 0 .05lJJa.
N
"E0 .04o
enl-I-
~ 0.03
t(J
0.02
FIGURE 8. SPECTRAL DISTRIBUTION OF ENERGY FOR PERFECT EMITTERS. THIS SHOWS THE RELATIVE CHANGE IN RADIATED ENERGY TO TEMPERATURE MEASURED BY THE INFRAREDTHERMOMETER (AFTER HARRIS AND WOODBRIDGE, 1966).
1--1 MINUTE 'I
25
RECORDED "FAST RESPONSE" TEMPERATURE
L:'ESPONSE LAG
RECORDED "SLOW RESPONSE" TEMPERATURE
"----' 33°C
TARGET REFERENCE TEMPERATURE (SHOWN DIAGRAMATICALLY)
FIGURE 9. LABORATORY TESTS OF REPEATABILITY, RESPONSE TIME,ANDACCURACY.
26
The magnitude of the noise response in Figure 9 was considered by
the factory to be "on the high side" but met their specifications. l
Expectable instrument response times are shown in Figure 10 as
provided by Dr. R. Lyons of the Stanford University remote sensing labo
ratory.
Field Application of Infrared Thermometer
The infrared thermometer is most efficiently utilized for detecting
thermal contrasts in shoreline waters by using a flying platform. Speed
. of surveying and ease of operation are primary advantages over sea-surface
measurements.
The resolution of sea-surface temperature measurements are directly
related to the speed of travel and to the response rate of the instrument
as discussed above and in Figures 10 and 11. Due to the improvement in
temperature accuracy with slowing of response time, a helicopter was used
for the instrument platform vehicle. 2 Typical operating velocities and
altitudes for the helicopter used are shown diagrammatically in Figure 11.
The planned field conditions were determined by comparison of data
shown in Figures 10 and 11. The 10-foot wide target area changing 8 times
per second would allow "fast" mode instrument response to about 65% of
the true temperature reading.
Maximum expectable resolution from the instrument and flying platform
limitations is the recording of 65% true temperature contrast in a body
of water 10 feet wide, and of greater than about 5 degrees temperature
contrast with the surrounding water. Smaller than 10-foot wide bodies
would be recorded with less temperature contrast proportional to their
size. Temperature contrasts of less than 5 degrees are masked by instru
mental "noise." Occasional noise peaks make positive detection of a 10
foot wide body of water (1/8 second exposure to thermometer) difficult,
if not almost impossible. However, contrasting temperatures of larger
springs (50 to 100 feet wide) should be detectable.
12
Personal communication, H. Maier, Barnes Engr. Co., December 1966.See Acknowledgements.
100
80
t 60wenzoa..enw0:: 40
20
oo 5
DOWN TO 2/3 AT 8.5 SAMPLES/SECONDi.e,~ 120 mSEC. SYSTEM RESPONSE
10 15 20 25 30
TERRAIN SAMPLES/SEC = 2 X CHOPPING FREQUENCY
35 40
N--.J
FIGURE 10. RESPONSE RATE OF INFRARED THERMOMETER. (AFTER DATA FROM R. LYON, STANFORD UNIVERSITY)
28
60MPH=88FT/SEC.- ~
"'----r-_,..........-
100'
- -10 FT. WIDE TARGET AREA...........~_ ...~~
FIGURE 11. DIAGRAM OF OPERATING VELOCITIES AND ALTITUDES FOR A HELICOPTER. THERESOLUTION OF SEA SURFACE TEMPERATURE RELATED TO PLATFORM HEIGHT,AND VELOCITY, AND TO THE I.R. THERMOMETER CONE OF VIEW AND RESPONSETIME. SLOWER OR LOWER FLIGHTS CAN ONLY BE ACCOMPLISHED WITH LOSSOF FLYING SAFETY.
29
Temperature Data Recording
To allow versatile handling of the data, the readout of the infrared
thermometer was recorded on magnetic tape. An automobile cartridge-type,
4-track tape playing mechanism was converted to record the 5- to 50-milli
volt temperature analog data as an FM signal and simultaneously record
voice field-note data on another track. Tape deck conversion involved
the installation of an in-line 4-track recording head on the tape recorder
mechanism as well as the FM recording electronics constructed by the
University of Hawaii's Institute of Geophysics electronic shops. Data
playback in the laboratory was done on a Crown 4-track tape deck fed into
a chart recorder. Voice data was transferred to the chart by hand.
FIELD TESTING
Electric Power and Helicopter Platform
Field testing of the infrared thermometer and recording unit was
done by mounting the sensor and recorder units and a battery-inverter
power source onto a stretcher attached to a Hawaiian Army National Guard
Helicopter (Figure 12).
Two flights were made over Oahu. The first traversed the central
portion of the island recording agricultural and land temperature en
route to the north shore where recordings were made on a zig zag course
along the shore from Kahuku to Kaneohe Bay. Only the most outstanding
temperature contrasts were recorded due to instrumentation problems
with the magnetic tape recording apparatus.
The second flight traversed the shoreline from Diamond Head to
Makapuu Point, and from Kaneohe Bay to Kahana Bay. Traverses were
done over Kahana Bay to record the temperature contrasts of coastal
springs and the outlet of Kahana Stream. The flight path is shown
in Figure 13.
RESULTS AND ANALYSIS OF PRELIMINARY FIELD FLIGHTS
Records obtained on the preliminary test flights confirmed expec
tations of the limitations of the instrumentation and served to eliminate
instrumental malfunctions. Usable records were obtained on each flight,
FIGURE 12. SHOCK-MOUNTED INSTRUMENTATION FOR FIELD TESTING. THE UNITS STRAPPED TO THESTRETCHER IN THE FOREGROUND ARE FROM LEFT TO RIGHTJ SENSORY HEADJ ELECTRONICSAND READOUT CONSOLE J FM MAGNETIC TAPE DATA RECORDERJ INVERTERJ AND BATTERY(PHOTO BY LARRY LEPLEY).
(,No
<.M.....
FIGURE 13. FLIGHT PATH OF PRELIMINARY TEST FLIGHTS.
32
but better records were made on the last flight due to improvements in'
the recording apparatus. In general, the infrared thermometer was found
to perform as specified in its design, but either the response rate or
elimination of instrumental noise should be improved.
Selected sections of the traverses indicate the good correlation
of records with ground features, but the difficulty imposed by instrumen
tal noise masks any but large areal and temperature anomalies of the
ocean surface at this time.
Infrared temperature profiling from residential housing to a for
ested area is shown in Figure 14. Major features such as houses, streets,
and lakes correlate well with the temperature profile. Variable emissi
vity of the objects may account for apparent anomalies such as the gen
erally high level of radiation from the forest area. Difficulties with
recording cross talk from the voice track to temperature data recording
(not shown on records) were corrected prior to the second flight. Tra
verses shown in Figures IS and 16 record both land and sea temperature
profiles. Figure IS records infrared temperature readings across sea,
beach, park,and urban areas with good recognizable correlation. Records
over the sea water show excessive fluctuation. Sea water with uniform
emissivity should provide relatively uniform radiation levels, and,
therefore, more steady temperature records.
The Hanauma Bay profile, Figure 16 reveals excellent general
temperature relations. Uniform land temperature with cool vegetation
change decreased about 4° to SOF over sea water. The noise, however, is
distracting and masks any local temperature anomalies.
Several solutions of the causes of the excessive noise are being
sought. Some noise is quite clearly instrumental, as shown by laboratory
testing, some may be related to the field conditions, and others may be
due to terrain radiation characteristics.
The instrumental noise appears to be caused by the detector or
preamplifier of the infrared thermometer and may be improved by compo
nent or circuit improvements or by refrigerating the components during
use .
Turbulent air from helicopter blades and forward flight air motion
may cause the apparent increase in field noise over laboratory test noise
levels. Extension of the sensor protective tube and use of conventional
~~-f!!~.!""·1~""~:!~!.a-'.~!~~Q9~~Q'-)~99"<::::79 Q ~~_9!)99399~Q~9 <i 9 9 <i 999~
NUUANU VALLEY
FIGURE 14. INFRARED TEMPERATURE PROFILE OF RESIDENTIAL AND FOREST AREA IN NUUANU VALLEY. A CORRELATION WITHTHE TERRAIN SHOWN DIAG~~TICALLY. MAJOR FEATURES, SUCH AS HOUSE ROOFS , SHOW DISTINCTLY BUT DETAIL IS COVERED BY INSTRUMENTAL NOISE.
c.Nc.N
Vol.;::.
LEWERSa COOKE
HONOLULU
FIGURE 15. INFRARED TEMPERATURE PROFILE OF SEA, BEACH, PARK, AND URBAN AREAS. A DISTINGUISHABLE CORRELATIONIS EVIDENT BUT THE VARIABILITY OVER WATER, WHICH SHOULD BE MORE CONSTANT WITH ITS GREATER UNIFORMITY OF EMISSIVITY, IS EXCESSIVE.
35
75°COOL
KOKO HEADPENINSULA
FIGURE 16. CORRELATION OF THE TERRAIN TO INFRARED TEMPERATURE PROFILE. CONSTANT EARTH TEMPERATURESBROKEN BY COOL VEGETATION, AND BY SEA WATERBECOMES PROGRESSIVELY COOLER AWAY FROM SHORE.POSSIBLE THERMAL ANOMALIES IN SEA WATER AREMASKED BY NOISE.
a i r craf t may help to eliminate these sources of noisy response.
Af t er the conclusion of fi eld tests i t was learned that similar
problems of instrument instability and noisy response were solved by
Mr. M. J. Doyle, Jr . , of the Pacific Gas and El ect r i c Company . He mea
sured warm water discharge from coastal power gener a t i ng plants. A
factory modification he reported effective was the installation of a
sealed detector to e l i mi nat e wind turbulence in the instrument. He
also installed a long wind isol ation tube on the sensor and used a light
Cessna aircraft gliding over the test ar ea to e l i minat e propeller tur
bul ence. He has made successful recordings of 1 degree temperature va
riations with these methods. Similar modifications to the Center's
instrument may a l so i mpr ove records.
A natural characteristic which may introduce noisy radiation records
over the sea is the specul ar reflection of sunlight by waves. Comparative
testing in sun and shade or at night should provide an evaluation of this
possibil i t y.
36
SUMMARY AND CONCLUSIONS
data on previously
flows which sig-
springs will provide
on changes in spring
fresh-water lens.
Hawaiian coastal springs are anticipated to be particularly amenable
to detection and mapping by synoptic sensors due to the large surface sa
linity and temperature anomalies found by field investigation. Infrared
scanners have successfully delineated some such springs (Fischer, et aZ.,
1964) and visible and near visible optical methods are being pursued.
Laboratory testing and preliminary flight testing of the infrared
thermometer with a National Guard helicopter has shown that heat sensing
is applicable to rapid reconnaissance detection of coastal springs and
that with innovated accessory equipment, it is adaptable to flight porta
bility.
Airborne mapping of offshore
unmeasured ground-water losses and
nal overuse of the Ghyben-Herzberg
ACKNOWLEDGEMENT
The authors gratefully acknowledge the valuable assistance rendered
by Hawaiian National Guard in providing the helicopter which made possible
the aerial traverses over the island of Oahu. The assistance of Generals
V. Siefermann and B. F. Webster in the arrangement of the helicopter
transport and Major Phillips, who piloted the aircraft, is deeply ap-
preciated.
37
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