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NBSIR 85-3131

Laboratory Design and Test

Procedures for Quantitative

Evaluation of Infrared Sensors to

Assess Thermal Anomalies

Y. May Chang

Richard A. Grot

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Gaithersburg, MD 20899

James T. Wood

DCS Corporation

Alexandria, VA 22314

June 1 985

QC'

100

U56

Prepared for: of Building Energy Research and Development

Department of Energy

ishington, DC 20585

85-3131

1985

NBSIR 85-3131

LABORATORY DESIGN AND TEST

PROCEDURES FOR QUANTITATIVE

EVALUATION OF INFRARED SENSORS TO

ASSESS THERMAL ANOMALIES

Y. May Chang

Richard A. Grot

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Gaithersburg, MD 20899

James T. Wood

DCS Corporation

Alexandria, VA 22314

June 1 985

Prepared for: Office of Building Energy Research and Development

U.S. Department of Energy

Washington, DC 20585

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

ABSTRACT

This report presents the description of the Laboratory apparatus

and preliminary results of the quantitative evaluation of three

high-resolution and two low-resolution infrared imaging systems.

These systems which are commonly used for building diagnostics

are tested under various background temperatures (from -20°C to

250 c) for their minimum resolvable temperature differences (MRTD)

at spatial frequencies from 0.03 to 0.25 cycles per milliradian.

The calibration curves of absolute and differential temperature

measurements are obtained for three systems. The signal transfer

function and line spread function at ambient temperature of

another three systems are also measured. Comparisons of the

dependence of the MRTD on background temperatures from the

measured data with the predicted values given in ASHRAE Standards

101-83 are also included. The dependence of background

temperatures for absolute temperature measurements are presented,

as well as comparison of measured data and data given by the

manufacturer. Horizontal on-axis magnification factors of the

geometric transfer function of two systems are also established

to calibrate the horizontal axis for the measured line spread

function to obtain the modulation transfer function. The

variation of the uniformity for horizontal display of these two

sensors are also observed. Included are detailed descriptions of

laboratory design, equipment setup, and evaluation procedures of

each test.

Key words: Background temperature; calibration curves; display

uniformity; infrared sensing systems; laboratory

evaluation; line spread function; magnification factor;

minimum resolvable temperature difference; modulation

transfer function; signal transfer function; spatial

frequency; target temperature.

i i i

TABLE OF CONTENTS

PAGE

Abstract m

List of Tables * vii

List of Figures..... viii

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

2. Description of Evaluation Facility 3

3. Quantitative Evaluation of Infrared Thermographic Sensors

Procedures and Results 7

3.1 Minimum Resolvable Temperature Difference (MRTD) 7

3.2 Temperature Calibration Curves 10

3.3 Signal Transfer Function (SiTF) 12

3.4 Optical Transfer Function (OTF) 14

3.5 Geometric Transfer Characteristics 16

3.6 Display Uniformity.. 17

4. Conclusions........ 18

5. Acknowledgements 19

6. References. ,...20

Tables 22

Figures * 33

Appendix A-1

V

LIST OF TABLES

Table 1. Specification of Building Diagnostic Sensors

Table 2. Instrument Items for the Evaluation Facility

Table 3. Test Target Sizes Required for Building

Diagnostic Sensors

Table 4. Parameters Evaluated for Each Infrared System

Table 5. Checklist for MRTD Testing of Sensors

Table 6. Parameters Determined from Absolute

Temperature Measurements

Table 7. Checklist for SiTF Testing of Sensors

Table 8. Temperature Windows from SiTF Tests^

Table 9. Temperature Shifts from SiTF Tests

Table 10.

1 Checklist for OTF Testing of Sensors

Table 11. Measurements and Results from ' On-Axis Magnification Test

Table 12. Results from Uniformity Test

V i i
LIST OF FIGURES

Figure 1

.

Figure 2 , Figure 3 .

Figure 4 .

Figure 5.

Figure 6 . Figure 7,

Figure 8a,

Figure 8b .

Figure 8c ,

Figure 8d

.

F igur e 8e .

Figure 9a,

Figure 9b,

Figure 9c ,

Overall Facility Concept

Basic Configuration for Test Sensor with Eyepiece

Basic Configuration for Test Sensor with Remote

Display Monitor

Overall Facility Setup for Imaging Systems with

Eyepiece

Overall Facility Setup for Imaging Systems with

Remote Display Monitor

Target Patterns Used for Various Tests

Minimum Resolvable Temperature Difference (MRTD)

Test Pattern in Target Module

Minimum Resolvable Temperature Difference (MRTD)

versus Spatial Frequency at Various Background

Temperatures T of System A (S=2)

Minimum Resolvable Temperature Difference (MRTD)

versus Spatial Frequency at Various Background

Temperatures T of System B (S=5)

Minimum Resolvable Temperature Difference (MRTD)

versus Spatial Frequency at Various Background

Temperatures T of System C (S=10)

Minimum Resolvable Temperature Difference (MRTD)

versus Spatial Frequency at Various Background

Temperatures T of System D

Minimum Resolvable Temperature Difference (MRTD)

versus Spatial Frequency of Systems A, B, C, D, and

E (Blackground Temperature T Cii 23°C)

Minimum Resolvable Temperature Difference (MRTD)

versus Background Temperature of System A (S=2)

for the Two ASHRAE Specified Test Frequencies

Minimum Resolvable Temperature Difference (MRTD)

versus Background Temperature of System B (S=5)

for the Two ASHRAE Specified Test Frequencies

Minimum Resolvable Temperature Diff erence (MRTD)

versus Background Temperature of System C (S=10)

for the Two ASHRAE Specified Test Frequencies

V i i i
Figure 9d. Minimum Resolvable Temperature Difference (MRTD)

versus Background Temperature of System D

for the Two ASHRAE Specified Test Frequencies

Figure 10. Image Display of System C for Pattern #4 at

Background Temperature of -170C

Figure 11a. Factor of Decrease for the Instrument Sensitivity

Versus Object Teipper ature of Systems A and D

(Using 30°C as Reference)

Figure lib. Factor of Decrease for the Instrument Sensitivity

Versus Object Temperature of Systems B and C

(Using 30OC as Reference)

Figure 12a. Absolute Temperature Calibration Curves of System A

at Various Background Temperatures T

(S=2, Aperture = f/1.8)

Figure 12b. Absolute Temperature Calibration Curves of System B at Various Background Temperatures T

(S=2, Aperture = f/1.8)

Figure 12c. Absolute Temperature Calibration Curves of System C

at Various Background Temperatures T (S=10)

Figure 13a. Differential Temperature Calibration Curves of System

A at Various Background Temperatures T (S=2)

Figure 13b. Differential Temperature Calibration Curves of System

B at Various Background Temperatures T (S=2)

Figure 13c. Differential Temperature Calibration Curves of System

C at Various Background Temperatures T (S=10)

Figure 14. Instrumentation Setup for Signal Transfer Function

(SiTF) Tests

Figure 15a. Relative Brightness versus Temperature Difference

from SiTF Test of System A at Constant Thermal

Level (TL=26.5) for Various Gains

Figure 15b. Relative Brightness versus Temperature Difference

from SiTF Test of System B at Constant Thermal

Level (TL=54) for Various Gains

Figure 15c. Relative Brightness versus Temperature Difference

from SiTF Test of System D at Maximum Thermal

Level (Brightness) for two gains (Contrast)

Figure 15d. Relative Brightness versus Temperature Difference

from SiTF Test of System A at Constant Gain (S=2)

for Various Thermal Levels

IX
Figure 15e. Relative Brightness versus Temperature Difference

from SiTF Test of System B at Constant Gain (S=5)

for Various Thermal Levels

Figure 16a. Line Spread Function (LSF) of System A as a Function

of Distance in Object Space

(S=2, TL=26, and AT=18°C)

Figure 16b. Line Spread Function (LSF) of System B as a Function

of Distance in Object Space

(S=2, TL=54, and AT=15oc)

Figure 17a. Modulation Transfer Function (MTF) of System A as a Function of Object Space Frequency

(S=2, TL=26, and AT=18oc)

Figure 17b. Modulation Transfer Function (MTF) of System B as a Function of Object Space Frequency

(S=2, TL=54, and AT=15°C)

X
1. INTRODUCTION

Over the past decade, infrared technology has been widely used as

a diagnostic tool to assess thermal anomalies in building

envelopes. Thermal patterns produced by the infrared imaging

systems provide rapid and useful information on thermal

performance of structures, and can be used to analyze the heat

loss and overall energy efficiency of buildings [1]. Due to the

complex and transient nature of heat flow through structures, it

is critical for the users to know the accuracy and parameters of

their equipment in order to assess the accuracy of their

measurements. Manufacturers of infrared sensing devices often

give specifications in their operating manuals and procedures for

calculating temperature measurement corrections from the given

parameters, such as sensitivity, thermal ranges, isotherm levels,

etc [2], These parameters are not sufficient to determine the

overall performance of the equipment. A good example is the

temperature dependence under various environmental conditions.

When using the infrared imaging systems for building inspections,

the difference between interior and exterior air temperatures

should be large enough to create enough heat flow for accurate

inspections. This implies that the colder the outside

temperature is, the more accurate the measurement should be.

However, for exterior inspections, as the outside air temperature

decreases, the sensitivity of instruments falls off much faster

than the increase of heat flow. As a result, the thermal image

produced by some sensing equipment under extremely cold outside

temperature will show no contrast [3],

Due to the fact that manufacturers have no standard

specifications for characterizing performance of infrared imaging

systems, it is difficult to predict the performance of sensing

devices in building diagnostic applications. For example,

"thermal sensitivity" sometimes is defined as the minimum

resolvable temperature difference (MRTD) at some unknown spatial

frequency, while other times it is described as MRTD with no

reference to frequency, or even is given as no i s e - e q u i v a 1 e n

t

temperature difference (NETD)*. Further, there is no laboratory

facility available in the USA to calibrate infrared imaging

systems and to compare their performance for building diagnostic

purposes. Therefore, it becomes necessary to test such equipment

under various temperature conditions prior to its use for

building diagnostic purposes. In general, the image evaluation

parameters which are meaningful for system specifications are: 1)

summary measurements; 2) signal transfer characteristics; 3)

geometric transfer characteristics; 4) spatial resolution; and 5)

noise characteristics. The first parameter involves human

interpretation of the image display of the sensor, and hence is

* NETD is defined as the blackbody target-to-background

temperature difference in a standard test pattern which produces

a s igna 1 - to-no i se ratio of unity.

1
the most critical factor, when the image is used for qualitative

measurements. In building diagnostic applications, the most

important summary measure is the MRTD which determines the

ability of an imaging system to detect thermal anomalies in

building envelopes.

Accordingly, the infrared image facility at the National Bureau

of Standards (NBS) was designed to test and evaluate infrared

imaging devices used in building inspections [4], The parameters

which are needed for evaluating the performance of an infrared

sensor* are: 1) the minimum resolvable temperature difference

(MRTD), which measures the capability of the compound observerimaging system to distinguish well-defined bar patterns on the

display as a function of temperature difference between target

and background; 2) the signal transfer function (SiTF), which

measures the signal gain of the sensor as a function of

brightness and gain controls and calibrates the dynamic range of

measurement windows; 3) the optical transfer function (OTF),

which measures the spatial resolution of a sensor based on the

Fourier Transform of the line spread function; 4) the geometric

transfer function, which measures the variation in local

magnification of a sensor across the horizontal f i e 1 d - o

f - v i e

w

(FOV)*"; and 5) the display uniformity of the detector, which

measures the variations in brightness across the display when the

sensor is viewing a un i f o r m- t em p e r a t ur e target. The functions

that the image evaluation laboratory is facilitated to perform

include: 1) determination of the parameters of sensors, 2)

comparison of the performance among candidate sensors, 3)

diagnosis of problems in available sensors, 4) evaluation of new

technology sensors, and 5) service as a central standard facility

for the building diagnostic community. In addition, the

calibration curves for absolute target temperatures as well as

differential temperatures at various conditions are generated.

Detailed description of the evaluation facility, test procedures,

and test results for instruments are discussed in the following

sections.

* In this report,

** FOV is defined

objects can be

when pointed in

a sensor is equivalent

as the total angular

imaged, recorded, and

a fixed direction.

to an imaging system,

dimensions with which

displayed by a sensor

2
2. DESCRIPTION OF EVALUATION FACILITY

The NBS infrared imaging evaluation (IE) facility which was

designed by the DCS corporation* under specifications by

researchers at NBS is dedicated to calibrate, evaluate, and

compare sensing devices presently on the market for building

diagnostics [4], Based on the documents in ASHRAE [5-7] and ASTM

[8-9] standards, and the choice of various characteristics, seven

sensors were originally selected as samples to be tested. Table 1 gives the summarized principle characteristics of these selected

sensing devices which are currently available or are expected to

be available in the near future with specifications for building

diagnostics. One of the existing environmental chambers at NBS,

whose dimensions are approximately 3m wide x 3m high x 6m long,

is utilized to provide ambient temperature simulated to actual

field conditions. The temperature range of the chamber is from - 20°C to 60°C (0°F and 140°F). The control room adjacent to the

chamber is used to control the temperature of the chamber, the

blackbody source and the remote monitor display, except for

sensors that use an eyepiece instead of remote monitor display.

For these sensors, the observer remains in the chamber.

The schematic of the overall facility is shown in figure 1. At

present, the instrumentation setup is complete except for a computer-controlled interface which is intended to be installed

in the future. The equipment required for the evaluation

facility was either purchased or constructed by the NBS machine

shop. Table 2 is a list of instruments that are required.

Detailed drawings of the hardware that were custom built by NBS

are contained in the appendix.

The ASHRAE and ASTM standards which are to be satisfied by the

test facilities are summarized below:

accuracy of differential temperature measurement between

source and background must be less than 0.1°C.

accuracy of source absolute temperature measurement must

be 1 ° C . distance between the target and the sensor must be

sufficient for the field of view of the sensor to

subtend a minimum area of 0.8m wide x 0.6m high in

object space.

MRTD test must include equivalent pattern sizes of 0.52

and 0.13 cycles/cm, for class A and class B surveys,

respectively

.

* Such identification does not imply recommendation or

endorsement by the Nationsl Bureau of Standards.

• The

• The

* The

* The

3
* The accuracy of luminance measurement of the display must be

sufficient to easily determine a shade of grey variation.

'Controlled environment must be able to relate to and

validate exterior measurement capabilities of sensors.

From the specifications of typical commerically available sensors

listed in table 1 further requirements of the characteristics of

sensors as well as other instruments of the NBS laboratory

facility are:

1) The blackbody source must be able to produce significant

temperature differences of 0.02°C, in order to test the

quoted sensitivity for sensors and to be consistent with the

standards

.

2) By using multiple objective lens configurations with the

imaging sensors to obtain approximately 20° horizontal FOV,

the ASHRAE/ASTM required test target sizes and distances

between targets and sensors were generated as given in table

3. Table 3 shows that all systems will fit within a 6m long

chamber, if they are required to meet the ASHRAE/ASTM MRTD

test and field of view constraints for interior survey work

(to cover minimum area of 0,8m wide x 0.6m high).

Furthermore, the requirement for a class B pattern, stated in

ASHRAE/ASTM Standards, can also be fit to a 13,5cm x 13.5cm

aperture on the heat source if everything is scaled down by a factor of two. There may be some focusing problems for

sensors which can be adjusted to a closer than publicized

near-focus distance.

3) The output coupling optics for making any measurements from

the display requires a compatibility to both infinite

conjugate (eyepiece) and finite conjugate (remote monitor)

displays. This is due to the fact that images from sensors

with eyepieces are either on a miniature 2,54cm CRT display

or real images of an LED array while those from sensors with

remote displays are on CRT for direct viewing,

4) The platforms must be able to handle weights up to 12 kg.

The basic configuration of major components of the laboratory

facility to test sensors with an integrated eyepiece can be

broken down into modules as illustrated in figure 2, Figure 3 is

a similar setup for testing sensors with remote displays. (Note

that all units, as well as display monitors are outside the

chamber.) According to figures 2 and 3, there are three modules

which contain 23 items for the laboratory setup:

1 ) Target/Source pattern module (which includes items 1-8):

Items 1-4: target /source table with mounting plate to

position target and background plate

4
Item 5: blackbody source to provide target radiation

Item 6: temperature controller for blackbody source to

indicate target, background, and differential

temperatures

Item 7: background plate

Item 8: target pattern holder.

2) Image sensor position module (which includes items 9-12 and 20)

S en s o r /mo n i t or table with mounting plate to position

sensor for viewing the target with horizontal, vertical,

and rotational movement capabilities.

3) Display monitor module (which includes items 13-19 and 21-23):

To measure relative brightness from the sensor's display.

mount e d outside or inside of the chamber.

Item 13: coupling lens to transfer image from the

display to the radiometric probe

Item 14: optical rail to be mounted external to the

chamber (when testing sensors with remote

displays) or internal to the chamber (when

testing sensors with integrated eyepieces)

Item 15: radiometric scanning eyepiece to scan signal

f rom display

Item 16: fiber optic cable to transfer light energy

to the photomultiplier tube

Item 17: photomultiplier tube (PMT) whose output is

being monitored

Items 18-19: digital radiometer with motor drive for

scanner to monitor signals from PMT

Items 21-23: remote monitor display table with mounting

plate and block to position monitor with

horizontal, vertical, and rotational

movement capability.

Future installation of a data analysis module is intended to

provide power to drive the facility components to various

positions. This module would also be capable of manipulating

output signals and presenting them in various formats and making

further calculations. Figures 4 and 5 are photographs to show

the overall facility setup at NBS for imaging systems with

integrated eyepiece and with remote monitors, respectively.

5
Among the selected infrared sensing equipment, only systems A and

B are properties of NBS. Quantitative evaluation of these two

systems has been completed. Due to the constraint of scheduling,

only partial measurements were made on some systems, and due to

unavailability, no test measurements were made on two systems.

Table 4 indicates the parameters that were evaluated for each

infrared sensing device.

6
3. QUANTITATIVE EVALUATION OF INFRARED THERMOGRAPHIC SENSORS

PROCEDURES AND RESULTS

3.1 Minimum Resolvable Temperature Difference (MRTD)

This important test evaluates the capability of the compound

imaging system-observer to resolve a well-defined bar target on

the display monitor at various temperature difference between

target and background (AT). It is used in b.oth the ASHRAE

standard 101-83 [7] and the proposed ASTM standard practice for

inspecting thermal defects in cavity wall insulation

installations [9]. By definition, the MRTD of a sensing device

is the lowest AT at which the pattern in a standard periodic 4-

bar pattern with aspect ratio of 7:1 is resolvable by observers

as a 4-bar pattern. During the test, there are no limits on

viewing time and no restrictions on thermal level and gain

controls. The MRTD is a function of both the s p a t i a 1 'f r e q u e n c y

of the bar pattern and the ambient temperature of the background

reference. The ASTM and ASHRAE standards have specifications on

minimum distance (1 meter) between the target and the sensor, and

minimum FOV (varies for individual sensors) for infrared imaging

systems. Accordingly, the distance between the sensor and the

target for each system is determined. Table 5 is a checklist for

the MRTD test for various imaging systems. Figure 6 shows all

target patterns constructed. Patterns #1 to #5, with target

spatial frequencies of 0.26, 0.52, 0.75, 1.04, 1.25 cycles/cm,

respectively are used for the test. Figure 7 shows one of the

patterns mounted in the target module. The source and background

plates must be matched with emissivities above 0.95 and have

controllable and measurable temperature difference below 0.02°C.

The imaging system is aligned with the tar ge t /ba ckgr ound so that

the bar direction is perpendicular to the scan direction, and the

displayed image is centered and in sharp focus, using AT = 5°C

and pattern #5, which is near the limit of resolution.

The procedure is to start with pattern #1, a very low input

frequency pattern, and a negative AT of magnitude great enough

to result in an image with four black bars. The observer

increases the AT in small increments (less than 0.1°G) until the

four black bars can no longer be distinguished from the

background. This value of AT =AT1 is recorded. The observer

increases AT until the four black bars first appear as white and

records the value of AT = AT2. The MRTD, for this particular

spatial frequency, is defined as the mid-point of these AT's,

i.e. MRTD = ( 1 / 2 )

• ( AT 2 - AT 1 ) . The brightness (level) and gain

(contrast) control settings of the sensor are also documented.

The same measurements are repeated for successively higher

spatial frequencies, patterns #2 to #5, to obtain the MRTD for

each pattern with brightness and gain controls remaining at the

same positions. If more than one person runs the test, the

results are averaged. Since the MRTD is often a function of

background temperature, the same test should be run by decreasing

the chamber temperature, from room temperature (— 25°C), to obtain

data sets as a function of temperature. As previously

7
prescribed, the control room outside of the chamber is utilized

to control the blackbody source temperature as well as the

display for such imaging systems with remote monitors. As for

sensors with integrated eyepieces, the entire setup is inside the

chamber

.

Five infrared sensing systems were evaluated for their MRTD

characteristics, of which three are h i g h- r e s o 1 u t i o n imaging

systems (HRIS A, B, and C) with remote display monitors, and two

are low-resolution imaging systems (LRIS D and E) with eyepiece

displays. These systems are all commonly used for building

inspections and their specifications are given in tdble 1. The

results of the MRTD tests are illustrated in figures 8a to 8e and

9 a to 9 d

.

Figures 8a to 8e show the MRTD versus spatial frequency of

systems A, B, C, and D at various ambient temperatures and a comparison of all five systems at room temperature. The expected

MRTD versus spatial frequency curve is such that at low spatial

frequencies the curve is fairly level and approaches the minimum

detectable temperature difference (MDTD)" of the system and at

some higher spatial frequency, there is a spatial frequency at

which the curve becomes a s ym t o t i c a 1 1 y vertical. Above this

frequency, the imaging system cannot be used to detect anomalies.

All systems exhibit this behavior, as shown in figures 8a to 8e.

System A indicates a stronger spatial frequency dependence than

systems B and C, As shown in figure 8a, at room temperature of

25°C, the MRTD of system A increases from 0.04°C, at the spatial

frequency of 0.03 cycles per milliradian, to 0.7®C, at a spatial

frequency of 0,15 cycles per milliradian. Figure 8b illustrates

that the MRTD of system B at 22°C room temperature at the same

spatial frequencies are 0.04°C and 0.4°C, respectively. As for

system C, the MRTD's observed at these spatial frequencies at

230C room temperature are 0.05°C and 0.2°C, respectively as shown

in figure 8c. Further, no asymptotic tendencies are noted at the

higher spatial frequencies of the MRTD curve for system C at this

ambient temperature (23°C), The MRTD curve at ambient

temperature of -7oc shows a slight tendency of a vertical

asymptote. However, when the ambient temperature dropped to - 15°C and below, the image display from system C of the bar

patterns has some type of distortion, as shown in figure 10, such

that no clear image can be observed to determine the MRTD.

Sources of such phenomenon, due to either the limitation of

instrumentation or defectiveness of instrumentation during tests

are not clear. The MRTD curves of systems A and B seem to become

vertical at a frequency slightly greater than 0,16 cycles per

milliradian, while the MRTD curves of system C indicate they are

still increasing monotonica 1 ly at 0.16 cycles per milliradian.

Therefore, the limiting spatial frequency of system C cannot be

estimated without testing this system at higher spatial

frequencies.

* MDTD is similar to MRTD except the target is a specified square

of uniform temperature distribution instead of 4-bar patterns.

8
Figure 8 d shows that the MRTD's of system D are higher than

systems A, B, and C and its limitation to detect anomalies is at

approximately 0.27 cy/mrad. Test results of system E indicate

that it has lower MRTD's than systems A, B, C and D at the high

spatial frequency range, as illustrated in 8e. At the low

spatial frequency range, the MRTD's of this LRIS seem to be

slightly higher than those of the HRIS. This implies that system

E under test at ambient temperatures of 24°C has better ability

to resolve temperature differences between sources and their

background for small objects than the other systems.

The temperature dependence of the MRTD of these HRIS's are shown

in figures 9a to 9d at the two spatial frequencies specified by

the ASHRAE standards. The MRTD for each imaging system increases

as the ambient temperature of the chamber drops which implies

that, for exterior inspections, the instrument sensitivities will

fall off as the outside temperature decreases. For example,

figure 9c illustrates that system C will not detect bar pattern

#4 at a chamber temperature below — 12°C and bar pattern #1 below

-18°C. The ASHRAE standard describes a theory developed to

explain this phenomenon of the MRTD [7]. From this theory a factor of decrease can be calculated for the instrument

sensitivity when the infrared sensing device is used at an object

temperature below 300C, the reference temperature. However,

using data from the laboratory measurements, the factor of

decrease for MRTD at various ambient temperatures below 30°C can

be obtained graphically. Since the values of temperature

difference (MRTD) are small (<10C) except using system D for

detecting pattern #4, the object temperature and background

temperature can be considered as the same value. The measured and

the theoretical factors of decrease are superimposed in figures

11a and 11b. The factor of decreasing sensitivity curves in

figures 11a and 11b for systems A, B, and C are using the average

values observed from patterns #1 and and for system D is

using data from pattern #1 only. By comparing the results of

systems with short wavelength (with spectral range from 3 to 5.6

urn), as illustrated in figure 11a, it can be seen that the

measured instrument sensitivity of system A agrees quite well

with the ASHRAE's calculated values. Figure 11a also indicates

that system D has better instrument sensitivity than that from

ASHRAE calculation [7], but the measured data are for detecting

low frequency pattern #1 only and they probably do not represent

its sensitivity for observing all spatial frequencies. By

comparing the results of systems with long wavelength (with

spectral range from 8 to 14 urn), as shown in figure 11b, the

measured instrument sensitivity of system B is slightly lower

than the ASHRAE calculated values except at extremely low

environmental temperatures (<-170C), where its sensitivity falls

off much faster . As for system C, its measured sensitivity was

found to be much lower than that from the ASHRAE theoretical

calculations at temperatures lower than 2°C. One possibility of

this discrepency in the behavior of system C with respect to the

ASHRAE theory may be attributable to the design of the unit which

is not accounted for by the emitted radiation theory assumed in

the ASHRAE standards.

9
3,2 Temperature Calibration Curves

By using infrared equipment for temperature measurement, the

numerical data received from the thermal radiation of an object

is often called the thermal value or thermal level in isotherm

units (lU), indicated on the front panel of the instrument. The

relationship between the thermal value and the object temperature

is non-linear and is sometimes given by the manufacturer as

graphical curves. Accordingly, the quantitative temperature of

an object can be obtained from the absolute temperature

calibration curves, which describe the relationship of object

temperature and the instrument's thermal level and the thermal

value. This calibration curve can be generated by using a square

pattern of 5,1 cm x 5,1 cm and the blackbody source to produce

accurate target temperatures from below ambient to above ambient

temperatures. The adjustment of isotherm controls will give the

isotherm units of the thermal level by brightening the target

image, (Detailed procedures are given by individual

manufacturers). In our laboratory experiment, the absolute

temperature calibration curves are generated at various ambient

temperatures, while the curves or data given by manufacturers are

often tested at room temperature of approximately 20°C, As a result, besides checking manufacturer's calibration curves,

temperature dependence of the infrared system for absolute

temperature measurement can also be established.

The results of this test for the three HRIS (systems A, B, and C)

at various chamber temperatures are shown in figures 12a to 12c,

The relationship between thermal value (in lU) and object

temperature for systems A and B is given by the manufacturers in

e q , ( 1 ) ,

C«exp(B/T)-l

where I is the thermal value in lU corresponding to T,

T is the object temperature in degree Kelvin (°K),

and A, B, and C are calibration constants for the settings

of the instrumentation.

Absolute temperature calibrations for system A were measured at

ambient temperatures from -20°C to 24°C, and they agree with the

calibration curve given by the manufacturer, which was generated

at a sole room temperature. Data points in figure 12a are from

measurements of three background temperatures, -20oc, -1°C, and

20°C, and from the comparison of these curves they do not show

any temperature dependence* The calibration curve from

laboratory measurements is determined by fitting the entire data

set to eq, (1) using regression analysis. However, absolute

temperature measurements from systems B and C do not have the

same behavior. System B was tested from -190C to 25°C ambient

temperature. Data points in figure 12b are measurements of

system B at background temperature -19oc, 1°C, and 25°C, and they

10
indicate a strong dependence on background temperatures and

exhibit noticeable temperature shifts from the manufacturer's

curve (tested at 22°C), especially at low ambient temperatures.

Data points at each background temperature were fitted to eq.

(1), as shown by dotted lines in figure 12b, Table 6 gives the

parameters from the manufacturer and those obtained by fitting

measured data of systems A and B to eq, (1), Note that these two

systems were tested for more than three ambient temperatures and

figures 12a and 12b only contain data for three temperatures.

Absolute temperature measurement dependence on background

temperature for system C is only observed at low ambient

temperatures, such that a significant temperature shift is

observed from -loc to -20°C and only a slight variation from 23°C

to -1°C, also shown in figure 12c, This may be due to a limitation of the system and related to the distortion observed

in MRTD test at low ambient temperatures. Also note that the

curve for system C is the relationship between the dial setting

of thermal level (rather than isotherm units) and object

temperature, which give lower values at high object temperatures,

as shown in figure 12c,

Another test of temperature calibration curves that can be done

is the temperature differential versus isotherm difference at

various environmental temperature conditions. This is useful for

many applications that require only differential temperatures.

This test also uses the 5,1 cm x 5,1 cm square pattern. By

changing the temperature difference of target to background ( AT)

at a constant thermal level, the isotherm difference

corresponding to each AT can be measured. The same test should

be run at various ambient temperatures to establish the system's

temperature dependence in measuring temperature differences.

The results of the differential temperature measurement for

systems A, B, and C at ambient temperatures from -20°C to 25°C

are shown in figures 13a to 13c, All systems have linear

responses of isotherm difference versus temperature difference

with the slopes related to the background temperatures. These

straight lines in figures 13a to 13c are determined by linear

regression for each data set, and the regression lines of fitting

the entire data set for each system are also included.
3.3 Signal Transfer Function (SiTF)

The purpose of this test is to verify and calibrate the dynamic

range of the sensors being used for thermography by measuring

their signal gain as a function of brightness and gain controls.

The curves generated from the SiTF test describe the output

luminance of a device at low spatial frequency as a function of

the input target signal ( AT) over the entire operating range.

The data from this test is obtained by increasing the input

target temperature differential from below ambient to a AT where

the system reaches saturation. As a result, the temperature

window for the contrast (gain) setting and the characteristics of

temperature shift^ing from level (brightness) control of an

imaging system can be established.

The target pattern used for SiTF test is a 5.1 cm x 5.1 cm square

aperature whose area subtends approximately 1% of the field of

view (FOV) of the sensors under test. The background plate

should fill the remainder of the FOV and combine with the

blackbody source of high emissivity. Figure 14 shows the

instrumentation setup for the SiTF test. A photometric probe

whose projected size is large compared to a scan line and small

enough to fall completely within the image aperature is used in

the Receiver Module to monitor the output luminance. Table 7 is

a checklist for the SiTF test for various imaging systems.

The test is conducted in the following way. Initially, with

pattern #6 (5.1 cm x 5.1 cm square) in position and the

differential temperature of source to background ( AT) equal to

5°C, adjust the target /background and s en sor /mon i t or tables at a distance according to table 7 and center the imaging of the

target on display. Prior to mounting the optical rail (item 14),

focus the image of the aperture target until it is sharp to the

eye. Mount the radiometric probe and the coupling lens as one

module on the optical rail, and make fine adjustment on this

module to position the probe aperture in the center of the square

target image. Next, cover the radiometric probe as well as the

coupling lens with heavy black cloth to reduce stray light. The

photomultiplier tube (PMT) and the digital radiometer should be

setup according to the manufacturer's recommendation and to give

an output signal well below the maximum when the brightness of

the display is at saturation. Generate SiTF by adjusting the

blackbody source from a negative temperature difference (AT

equals about -5°C) to a value at which the output signal is

saturated. Record both values of AT's and relative brightness

output from the radiometer. Repeat the similar measurement for

various combinations of brightness (level) and gain (contrast)

settings of the sensor by using approximately three settings

(maximum, mid-point, and minimum) of each. Therefore, the SiTF

of different gains at a fixed brightness, and various brightness

at a constant gain are measured.

The results from the SiTF test for systems A, B, and D are shown

in figures 15a to 15c which illustrate the relative brightness

12
from the radiant as a function of the temperature difference

between the background and the target of these three systems.

System A was tested at thermal levels in isotherm units (lU) of

2 2, 26 .5 , and 28 with gain settings at S = 2, S = 5, and S = 10.

System B was tested at thermal levels of 50, 54, and 56 with gain

settings at S = 2, S = 5, and S = 10. System D, which does not have

any marked settings, was tested at approximately maximum and

midpoint of contrast with maximum brightness. When testing system

D at brightness setting less than the maximum and the contrast

setting at minimum, the output signals failed to reach saturation

even with AT greater than 15°C.

The linear regions of these SiTF curves are determined by using

linear regression analysis. Number of data points as a function

of goodness of fit is compared to fit data at the most points of

each curve. The temperature windows corresponding to each

contrast setting at various thermal levels can be established

from the regression line as it goes from 1% to 90% of the maximum

brightness (at saturation) of the SiTF curve. The linear region

of temperature shifts from changing thermal levels can be

obtained from the shifts at the midpoint of these regression

lines for each contrast setting. The results of the temperature

windows and temperature shifts for the imaging systems are given

in tab 1 es 8 and 9.

Table 8 shows that the variation of temperature windows at

different thermal levels of both systems A and B are between 15%

and 30% at each gain setting, and five of them are measured to be

higher and only one lower than the indicated sensitivities of

S=2, S=5, and S=10. As for system D, the difference in

temperature windows at gain setting from maximum to mid-point was

found to be approximately 1°C. Table 9 indicates that the

temperature shifts from various gain settings of both systems A

and B are between 5 and 20 percent at each thermal level setting,

and they are all higher than the changes of the indicated levels.

13
3,4 Optical Transfer Function (OTF)

The OTF describes the ability of an imaging system to reproduce

the spatial frequency content of the target. In general, the

image differs from the target with amplitude attenuation and

phase shift. The purpose of the OTF test is to obtain a continuous curve to measure the system response as a function of

spatial frequency for the imaging system based on the Fourier

Transform of the line spread function (LSF). It is an objective

measure of maximum resolution of a sensor in a linear operating

mode at a high radiance level, which should correlate with the

high frequency asymptote of the MRTD curves. Therefore, it is

necessary to insure that the imaging system being tested is

operating in its maximum linear region, and that the region of

measurement is sufficiently isoplanatic. The LSF generated by a narrow slit can be measured by the- scanning method to give its

intensity distribution of the LSF of the narrow slit. The

Fourier Transform of the measured LSF, which is defined as the

OTF, has two terms; the modulus (amplitude) and the argument

(phase). The modulation transfer function (MTF), which is the

modulus of the Fourier transform, determines the amplitude

response of the imaging system. In the NBS facility, a scanning

slit probe is used to perform the measurement of LSF of the

narrow slit target.

The OTF test setup is similar to the SiTF test (shown in figure

14) except that the positions of the coupling lens are reversed,

a different target pattern (0,25 mm slit) is used, the scanning

probe is replaced with a smaller scanning slit probe (0,075 mm),

and a scanning motor with a control box for moving the slit probe

is used. According to the size of the slit, the distance between

target and sensor has to be adjusted so that the angle subtended

by the slit width is much smaller (about ten times) than the

instantaneous field of view (IFOV)* of the system being tested.

Table 10 is a checklist for the OTF test for various imaging

systems. The steps are listed below. Follow the same procedures

as in the SiTF test to align the radiometric slit probe with the

camera lens, to focus the slit image of the slit target, and then

to position the probe horizontally until the probe's slit

aperture falls in the center of the slit image of the slit

target. In order to provide a high level of radiation from the

source and to operate the system in the linear region, generate a modified SiTF curve at the peak of the output slit spread

function for various combinations of brightness and gain controls

to determine the linear region (by similar procedures as SiTF

test). Afterward, adjust the blackbody source to the AT value

found at the end of the linear region (about 20% of the AT which

leads to curve saturation). Use the scanning motor to move the

* IFOV is the angle in mrad determined by dividing the size of

the sensor's detector by the effective focal length of the

sensor's objective lens and multiplying by 1000.

14
slit probe from one end of the image to the other by controlling

the probe's positions from the control box. Record the output

signal from the digital radiometer at each position of the slit

probe as these values represent the measured LSF. The MTF can be

obtained by taking the Fourier transform of the LSF.

The LSF was measured for systems A and B. After the modified

SiTF was generated to locate the linear operational region for

the slit image and the slit probe, the differential temperature

( At) for systems A and B was determined to be 18°C and 15°C

respectively. By using these AT'^s, the LSF could be generated

from the relative brightness of the radiometer (at such AT) as a function of slit probe's position while the probe is moving from

one end of the image to the other. The LSFs of both systems are

shown in figures 16a and 16b, The measured LSF was originally in

millimeters from the position of the slit probe. It should be

calibrated to milliradians in object space for output image of

the infrared devices. The calibration is based on the

magnification factor of the imaging equipment and the focal

lengths of the coupling lens which can be established from the

on-axis magnification test described in the next section.

The LSF shown in figures 16a and 16b can be analyzed by

estimating the width of the function at its half amplitude

points. The inverse of this value is a good indication of

maximum resolution of an imaging system operating in its linear

range, which corresponds to the vertical asymptote of the MRTD

curves. The spreads at half amplitude points of systems A and B are found to be 5,8 mrad and 6,65 mrad, respectively.

Accordingly, the maximum resolutions of these two systems are

calculated to be 0.17 and 0,15 cy/mrad, which agree with the MRTD

curves in figure 8.

The MTF of the imaging system is determined by using the

algorithm of Fast Fourier Transform [10] and numerical analysis

in order to locate the modulations other than the harmonics and

to check the modulations at l;iarmonics by both methods. The

results for both systems are in agreement and are presented in

figures 17a and 17b, As illustrated in figures 17a and 17b, the

spatial frequency range at which the modulation reaches 0.05 to

0.02 is between approximately 0.15 and 0,2 cy/mrad, which agrees

with the maximum resolution of these systems. By using the

instantaneous fields of view (IFOV) given by the manufacturer

(IFOV = 3.5 mrad), the nominal mid-frequency f^ (which is defined

as 1/2(IF0V)) of systems A and B is equal to 0.14 cy/mrad.

However, the MRTD curves of these two systems (A and B) indicated

that they are approaching the asymptote at this spatial frequency

(f = 0,14 cy/mrad) and the nominal mid-frequency range should be

between 0.1 and 0,12 cy/mrad. In this case, the IFOV of these

systems are in the range of 4 to 5 mrad, and the modulation of

systems A and B are in the range of 0.2, indicating they are

we 1 1 -de s igne d systems.

15
3.5 Geometric Transfer Characteristics

This test is to measure the on-axis magnification of the infrared

imaging devices across the horizontal FOV in order to calibrate

the horizontal axis in milliradians in object space. The

laboratory setup is similar to the OTF test except the object is

bar pattern #2 or #3 instead of a slit. The input object's

subtended angle in milliradians can be calculated by the known

dimensions of the bar pattern and the distance between the target

and the sensor. The output image size in milliradians can be

measured by scanning the slit probe to obtain the distance

between a peak and a valley of the scanned bar pattern image,

which represents the length of a half cycle. The output from the

digital radiometer is converted to the size on the monitor by

multiplying the output data with the ratio of focal lengths of

the coupling lens. The on-axis magnification of the imaging

system is then given as the ratio of the output image to the

input object space size, either in mm/mrad or mrad/mrad,

depending on the individual system.

The calculation of the magnification factor of an imaging system

should use the following steps: Let the half-cycle input size in

object space be mrad, and the measured distance between a peak

to a valley from the radiometer be nun. The distance from the

peak to the valley of the image on the monitor W 2 in mm is

calculated as

V?2 = W 3 -(fi/f 2

) (2)

where f and f£ nre the focal lengths of the coupling lens with

lens #1 backing to the monitor and lens #2 backing to the slit

probe. Therefore, the magnification for the imaging equipment is

given as

M - (W 2 /W 2

) mm/mrad (3)

and the magnification for the sensor and lens is given as

= (W3/W^) mm/ mrad (4)

Both patterns #2 and #3 were employed to test for on-axis

magnification of systems A and B. The average values obtained

from both patterns are used to calibrate the horizontal axis for

the LSF. Table 11 gives the measurements and results from the

magnification test.

16
3.6 Display Uniformity

The purpose of this test is to measure the large and small scale

variations in brightness across the display when the imaging

devices are viewing an object/scene of uniform temperature. This

measurement is the primary interest for building diagnostics.

The setup for this test is similar to the SiTF test except that

the entrance aperture of the sensor under test is covered with a heavy black cloth to provide uniform input for the sensor. The

output can be measured by scanning the radiometer probe across

various regions of the display, manually or with a motor drive.

In the laboratory setup, the Uniformity Test was run on systems

A and B, for horizontal displays only with results shown in table

12. As shown in table 12, the average standard deviation of the

mean is 5.4% and 5.7% of the average output for s.y stems A and B,

respectively. The uniformity display of these two sytems is

considered to be good, since their large scale variations across

the horizontal display are less than 6% of the average signal

output at maximum gain, (S=2).

17
4. CONCLUSIONS

Five infrared imaging systems (A, B, C, D, and E) were tested to

evaluate their performance for building diagnostics, of which two

systems (A and B) have complete sets of test results.

The MRTD test indicates that all sensors are spa t ia 1 -frequency

dependent as well as temperature dependent and the instrument

sensitivities of systems A and B are in agreement with ASHRAE's

calculations, while that of system C is not. The absolute

temperature measurement reveals that data of system A is not

temperature dependent, in agreement with the manufacturer's

curve, while data of both systems B and C exhibit temperature

dependencies, and temperature shifts from the manufacturer's

curve for system B at room temperature (no curves available from

the manufacturer of system C). The differential temperature

measurement shows that thermal levels of systems A, B, and C

respond linearly to temperature differences between target and

background.

Measurements from SiTF depict that system A has smaller

temperature windows than system B at identical sensitivity

settings; while system B has less temperature shifts than system

A at equivalent changes in thermal levels. Tests from OTF

indicate almost identical MTFs are obtained for both systems A

and B. The maximum resolution of these two systems are in

agreement with results from the MRTD test. However, the

estimated IFOV from MTF has a discrepancy from values given by

the manufacturers.

Results from on-axis magnification tests are used for

calibration of the horizontal axis for the OTF test. Data from

the uniformity test suggest that both systems A and B have fairly

uniform horizontal displays.

The results from the above laboratory evaluation give general

characteristics of each of the imaging systems under test. Due

to the unavailabilities and time constraints of several sensing

systems, complete test results for all systems except A and B are

not available. It is intended to investigate the performance of

other systems at a later time, and such investigations may also

include quantitative measurements other than those reported here.

18
5. ACKNOWLEDGEMENTS

This work wa

interagency

Interagency

Modification

s supporte

agreement

A g r e em e n t 38.

d by

with

No.

the Department of Energy

the National Bureau of

DEAI 01-76 PRO 6010,

through an

Standards

,

Task #008,

The authors

of Douglas

Lane. Both

laboratory

would like to acknowledge the technical contributions

Pruitt and the effort of Phillip Engers and Patrick

are cooperative education students who assisted in

tests.
6. REFERENCES

[1] Wood, J.T., Cuttica, J.J. and Snow, F.J., "Application of

Imaging Evaluation Technology Sensors to Heat Loss

Diagnostic Sensors", Modern Utilization of Infrared

Technology V, Proc. SPIE Vol. 197, pp. 108-114, Bellingham,

WA, 1979.

[2] Kaplan, H., "An Update of Commercial Infrared Sensing and

Imaging Instruments", An International Conference on Thermal

Infrared Sensing for Diagnostics and Control (Thermosense

VI) Proc. SPIE Vol. 446, pp. 239-246, Bellingham, WA , 1983.

[3] McIntosh, G.B. and Filippene, A.F., "Minimum Resolvable

Temperature Difference (MRTD) Testing: Equipment

Specification for Building Performance Diagnostics", Thermal

Infrared Sensing Applied to Energy Conservation in Building

Envelopes (Thermosense IV), Proc. SPIE Vol. 313, pp 102-111,

Bellingham, WA , 1981.

[4] Wood, J.T. and Grot, R.A., "Description of a Facility for

Evaluating Infrared Imaging Systems for Building

Applications", Thermal Infrared Sensing Diagnostics

(Thermosense V), Proc. SPIE Vol. 371, pp. 146-149,

Bellingham, WA , 1982.

[5] Burrer, G.J., "Update on Proposed ASHRAE Standard on

Requirements for Infrared Surveys", Thermal Infrared Sensing

Applied to Energy Conservation in Building Envelopes

(Thermosense III), Proc. SPIE Vol. 254, pp. 148-153,

Bellingham, WA , 1980.

[6] Snow, F.J., "American Society of Heating, Refrigeration, and

Air Conditioning Engineers (ASHRAE) Thermographic Standard

lOlP", Thermal Infrared Sensing Applied to Energy

Conservation in Building Envelopes (Thermosense IV), Proc.

SPIE Vol. 313, pp. 94-98, Bellingham, WA, 1981.

[7] ASHRAE Standard 101-83, Application of Infrared Sensing

Devices to the Assessment of Building Heat Loss

Characteristics, ASHRAE, Atlanta, GA , 1983.

[8] Wood, J.T., "Evolving American Society for Testing and

Materials (ASTM) Procedures on Use of Infrared (IR) Imaging

Devices for Building Diagnostics", Thermal Infrared Sensing

Applied to Energy Conservation in Building Envelopes

(Thermosense III), Proc. SPIE Vol. 254, pp. 154-158,

Bellingham, WA , 1980 .

[9] Kantsios, A.G., "Progress on American Society for Testing

and Materials (ASTM) Practice on Thermographic Inspections

of Wood Frame Buildings", Thermal Infrared Sensing Applied

to Energy Conservation in Building Envelopes (Thermosense

IV), Proc. SPIE Vol. 313, pp. 99-101, Bellingham, WA, 1981.

20
f •

[101 Ahmed, N. and Rao, K.R., Grthegea&l Taaiafea^

Siftn&l Rg»eeas4:Rg . Berlin - Heidelberg: Springer1975, ch. 4, p. 79.

B jrgifea 1 V e r 1 a g ,

:• iu *'

:?V-‘

.f.

TZ^

i?*rrv ru-Jh»«iQ^ _ -V.

,

f« « • r * r « .*

KS^i

* \-r

y

t i

25. Cor,, :

1 I 5 '

f ' ;

* 1
Table T Specifications of Building Diagnostic Sensors

IR System

DATA

DESCRIPTION

A

B

(Dual Channel)

C D E F G

Field of View w/33mm lens 20°x20° NFOV

40°x40° WFOV

14°xl8° 7.5°xl8° 6 xl2 w/50mm lens 20°x20° NFOV

40°x40° WFOV

w/2.5X afocal 6.8°xll.2° NFOV

19°x28° WFOV

Instantaneous

Field of View

3.5 mrad NFOV

7.0 mrad WFOV

2.0 mrad 2.2 mrad 2.0 mrad 2.4 mrad NFOV

4.8 mrad WFOV

0.73 mrad NFOV

1.8 mrad WFOV

F// 1.8 - 1.5 1.0 - 1.0 EFL 1.3" NFOV

0.7" WFOV

- 1.5" 2.5" - 2.75" NFOV

1.1" WFOV

Additional

Optics

52mm

99mm

191mm

3X afocal

lOX afocal

None None 100mm

75mm

5X afocal

Display AGA CRT

(5" diag)

525 line CRT Monocular

Eyepiece (LED)

Monocular

Eyepiece (CRT)

525 line CRT 525 line CRT .

Detector Type

and Number

1 InSb (3-5.6)

1 HgCdTe (8-14)

HgCdTe 6 InSb 48 PbSe DTGFB(PEV) 2 HgCdTe

Spectral

Range

3-5.6 microns

8-14 microns

8-12 microns 3-5.4 microns 3-5 microns 8-12 microns 8-12 microns

Interlace 4:1 2:1 10:1 1:1 - 2:1

Quoted

Sensitivity

0.1°C @ 30°C

100 Pixels/line

0.1°C MDT

(a 30°C

150 pixes/line

0.1° NET

(peak-to-rms)

0.2°C (peak) 0.2°C NET

@ 8LP/mm

0.2°C NET

0.4°C MRT

0 0.27 c/mr

Size and

Weight

Scanner:w/o lens

7 lbs. 9,3"xl0.2"x6.5"

24 lbs. Scanner:4 lbs. 6.1"x4.3"x4.8"

(w /battery)

7.5 lbs. 10"x9"x6"

6.6 lbs. 9.4"x5.5"x3.3" (w/o battery)

Camera:w/o lens 24 lbs. 10"x8"x8"24 lbs (total) Scanner:! 1 lbs. 10.7"x7.3"x9.1" Power

Requirements

100, 120, 220,

240 VAC

8-15 VDC

12 VDC or 110 VAC

1.5 W

Battery Charger:

117 VAC

6 VDC

110/220 VAC

115 VAC 12 VDC

110 VAC

Operating

Temperatue

Range

-15°C/+55°C - - -20°C/+55°C -32°C/+49°C -15°C/+55°C

Cooling Cryogenic

(liquid

nitrogen)

Cryogenic

(liquid

nitrogen)

3-T Cryostat Split Sterling None 3-T Cryostat

Minimum

Focus

20 cm (WFOV) 13 cm 200 cm 100 cm 244 cm 150 cm

NFOV : N o rm a 1 Fie Id o f View

WFOV : Wide F i e 1 d 0 f View

F# : Aper tu r e EFL : Effe c t iv e Fo ca 1 Length

Conv er s ion Fa c t or s f 0 r SI Units : 1 in

0.4536 kg

2,54 cm

22
Table 2 Instrument Items for the Evaluation Facility

1 1 em

1. Target Source Table

2. Vertical Motion Jactuator

3. Target Source Mounting Plate

4. Source Mounting Block (Wood)

5. Blackbody Source

6. Blackbody Source Controller

7. Background Plate

8. Target Pattern Holder

9. Sensor /Monitor Table

10. Sensor /Monitor Rotating Table

11. Sensor /Monitor Mounting Plate

12. Sensor Mounting Block

13. Coupling Lens (2)

14. OpticalRail (Modified)

15. Radiometric Eyepiece

16. Fiber Optic Cable

17. Photomultiplier Tube

18. PMT Power Supp ly / Signa 1 Monitor

19. Motor Control Scanner

20. Casters

21. Display Mounting Block (Wood)

22. Display Rotating Table

23. Display Mounting Plate

24. Refrigerator System for Chamber

25. Computer Facility (Future Items)

Status

Constructed

Purchased

Constructed

Constructed

Purchased

Purchased

Constructed

Constructed

Constructed

Pur cha se d

Constructed

Cons true ted

Purchased

Available in-house

Pur cha se d

Purchased

Purchased

Purchased

Purchased

Purchased

Constructed

Available in-house

Constructed

Available in-house

Available in-house

23
Table

3.

Test

Target

Sizes

Required

for

Building

Diagnostic

Sensors II

(Uuc

fO awc

V*£

'3

t-* <0c

k.

•u

•«->

(fl CL

<v

tiC l.

ASHRAE Class B

.13 .13 .13 .13 .13 .13

ASHRAE Class A

/ASTM (N <N1 (N (N (N (N

ir\ vr\ vrv lOi ir\

(N ^ (N1 CTN . <1- <t 00 ^ >0\ 00 l/> o ON ^ vo fN m • —••••• t —< fN

OJE r»^ ir\ ij- 1^ (N 4-» 00 <N ^ \D VO c o rv (M VO O CV U • •••••

t/i V ON 00 o 00 -a- ON u .. (N oo o m \o

>> vO Ov lo, ^ 00 u

VO •a- fO vO «A (N 00

(N CM

—1

VO

—< o 0 irv 00 fO po

MH

(N lA iSO OV

-H ON IPN

—< (N 00

O PO

J3- (N CM ^ hv • •••••

IV. tOi ON PO CM

.O- CM

O

—< ON o —M CM —< —• CM m >n to o CM o -a- 00 U i_ • ••••• fc E

pPi (N CM CM CM—

c P, ti P O P^ O O il* o .3 U ^ lA O O «PN s £ S ^ (Vj _ (SI —. • c —

+J

C

—. c rv pr\ ir\

—( r«v <2 o fl h (M ir\ IPS hv <M IS. Q £ ^ w CM CM .a- u-\ CM —

. J= ^ c r:: *C P O O <3- O O 00 ^ ^ ,, 00 00 .a- CM 00 00 S ^ ^ - o o o 8 o o > O 00 —' o O 00

r\ CM

—< J< (M CM CM

W

X

X

O -H

X

X

u«

OO

X o o o -a- • o o ov

(M

—< vO (M—< s ca

UJ

f- t: kO

>-

ai c D E F

G

to <

24
Table 4 Parameters Evaluated for Each Infrared System

Parameter

Evaluated

IR System

A B C D E

Minimum Resolvable

Temperature Difference (MRTD) X X X X X

Temperature Calibration X X X

Signal Transfer Function (SiTF) X X X

Optical Transfer Function (OTF) X X

Geometric Transfer Function (GTF) X X

Display Uniformity X X

25
Table 5 Checklist for MRTD Testing of Sensors

IR System

Facility

Component

. Number A

B

C D E F G

1 - 6 X X X X X X

7 * X X X X X X

Use Use Use Use Use Use

H H V V H V

Marks Marks Marks Marks Marks Marks

S X X X X X X

w/Patterns w/Patterns w/Patterns w/Patterns w/Patterns w/Patterns

//I - ^^5 01 - 05

Repeat

03 - 05

01 - 05 0 \ - 05 0 \ - 05

Repeat

03 - 05

01 - 05

Repeat

02 - 05

9-12 X X X X X X

Estimated 45.4" 50.5" 91.5" 114.5" 45.4" 35.9"

Distance or or or or or or From Tgt

to Sensor

115 cm 128 cm

Retest at

101"

or 256 cm

232 cm 291 cm 115 cm

Retest at

90.8"

or 230 cm

91 cm

Retest at

107.7"

or 274 cm

Focus

Pattern

05 05 05 //4 05 05

"Use H Marks" means to use the marks which mark the horizontal

Field of View limits on the Background Plate (See Insert in

Figure 1) when setting the distance between the Target Pattern

and the Sensor under test.

Mark (x) means to make sure the facility components are in place

and used as indicated.

26
Table 6 Parameters Determined from

Absolute Temperature Measurements

System Background Parameter s Temperature (°C)

A B* C*

A -20 201126 2550 1 .70

( S = 2 ) -1 290189 2716 1.31

13 318218 2755 1 . 23

24 351344 27 97 1.17

All Data 333889 2818 1 .04

Given by 552855 2994 1.0

Manufacturer

B -20 10328 1052 5.22

(S = 2)

1 23208 1274 5.74

5 29549 1318 6.42

14 26623 1306 5.99

25 39234 1394 6.79

Given by 22 -3762 1510 -0.45

Manufacturer

A, B, and C are instrument parameters given in eq. (1).

27
Table 7. Checklist for SiTF Testing of Sensors

IP System

Facility

Component A C D F F G

Number B

1 - 7 X X X X X X

8 X X X X X

’ X

w/Pattern w/Pattern w/Pattern w/Pattern w/Pattern w/Pattern

//6 //6 y/6 //6 -//6' //6

9-12 X X X X X X

13 X X X X X X

Lens 1 Lens 1 50mm 24mm Lens 1 Lens 1 100mm 100mm 100mm 100mm

and and and and

Lens 2 Lens 2 Lens 2 Lens 2

24mm 24mm 24mm 24mm

14 X X X X X X

15 X X X X X X

.018" .018" .018" .018" .018" .018"

Scanning Scanning Scanning Scanning Scanning Scanning

Probe Probe Probe Probe Probe Probe

16 - 18 X X X X X X

Distance 45" 101" 91.5" 114.5" 90.8" 107.7"

From Tgt or or or or or or

to Sensor 115 cm 256 cm 232 cm 291 cm 230 cm 274 cm

"Use H Marks" means to use the marks which mark the horizontal

Field of View limits on the Background Plate (See Insert in

Figure 1) when setting the distance between the Target Pattern

and the Sensor under test.

Mark (x) means to make sure the facility components are in place

and used as indicated.

28
Table 8 Temperature Windows from SiTF Test

SYSTEM THERMAL

LEVEL

TEMPERATURE WINDOWS OF SENSITIVITY (GAIN)

(°C)

S = 2 S = 5 S = 10

22 2.55 6.25 9.87

A 26.5 2.35 5.11 8.58

28 2.10 4.71 8.40

50 3.20 7.12 12.76

B 54 * 6.68 11.87

56 2.70 6.47 11 .48

Gain = MAX Gain = l/2( MAX

)

D MAX 2.93 3 .77

* Missing data

Table 9. Temperature Shift from SiTF Test

SYSTEM

CHANGE IN

THERMAL LEVEL

TEMPERATURE SHIFT OF SENSITIVITY (GAIN)

(°C ) S=2 S=5 S=10

A

22 - 26.5

26.5 - 28

22 - 28

6.0 5.9 5.5

2.4 1.9 1.7

8.4 7,8 7.2

B

50 - 54

54 - 56

50 - 56

* 4.5 4.6

* 2.3 2.0

7.0 6.8 6.6

Missing data

29
Table 10. Checklist for OTF Testing of Sensors

IR System

Facility

Component A

B

C D E F G

Number

1 -7 X X X X X X

8 X X X X X X

w/Pattern w/Pattern w/Pattern w/Pattern w/Pattern w/Pattern

in in in in in in

9-12 X X X X X X

13 X X X X X X

Lens 1 Lens 1 200mm 100mm Lens 1 Lens 1 24mm 50mm 100mm 50mm

and and and and

Lens 2 Lens 2 Lens 2 Lens 2

100mm 100mm 50mm 100mm

14 X X X X X X

13 X X X X X X

.003" .003" .003" .003" .003" .003"

Scanning Scanning Scanning Scanning Scanning Scanning

Slit Slit Slit Slit Slit Slit

16 - 18 X X X X X X

Distance 45" 101" 91.5" 114.5" 90.8" 107.7"

From Tgt or or or or or or

to Sensor 115 cm 256 cm

« 232 cm 291 cm 230 cm 274 cm

* "Use H Marks" means to use the marks which mark the horizontal

Field of View limits on the Background Plate (See Insert in

Figure 1) when setting the distance between the Target Pattern

and the Sensor under test.

Mark (x) means to make sure the facility components are in place

and used as indicated.

30
Table 11 Measurements and Results from

On-Axis Magnification Test

System A System B

Pattern Pattern

#2 #3 #2 #3

Input

Target W 2

( mr a d

)

8.77 5.80 8.77 5 . 80

Output

Slit W 2 ( mm

)

5.80 3.60 4.70 3 .075

Position

Image on W 2 ( mm

)

1.392 0.868 1.128 0.738

Monitor

M (mm/mrad) 0.16 0.15 0.13 0.13

* Average M ( mm / m r a d ) 0.155 0 .13

M 2 * * ( mm / mr a d

)

0.65 0.54

Magnification factor of IR system.

Magnification factor of IR system and lens.

31
Table 12 Results from Uniformity Test

Thermal Level

Average Relative

Brightness

Standard Deviation

of the Mean

Percentage of

Variation

System A Sy s t em B

26 28 54 56 58

31.21 30.48 31.66 31.66 31.01

1.70 1 .65 1.77 1 . 82 1.82

5.40 5.40 5.60 5.75 5.88

Average Percentage 5.40 5.74

of Variation
INFRARED

THERMOGRAPHIC

LABORATORY

33

Figure

1.

Overall

Facility

Concept
INFRARED

THERMOGRAPHIC

LABORATORY

>

34

Figure

2,

Basic

Configuration

for

Test

Sensor

with

Eyepiece
INFRARED

THERMOGRAPHIC

LABORATORY o

l-l Ocos

Sn

CO

c- • CD • HQ

QJ

j-l 0B

01 ai

x:3

Vj0wC

01

CO

o; H

)-i o

U-lco

CO

)-i 3

oc • ^

CMco

CJ

CJ • CO

CO CQ

oc 3 5
For MRTD Test

For Other Tests

Figure 4

.

Overall Facility Setup for Imaging Systems

with Eyepiece

36
Inside Environmental Chamber

Figure 5 . Overall Facility setup for Imaging Systems

with Remote Display Monitor

37
Figure 6 Target Patterns Used for Various Tests

Figur e 7

.

Minimum Resolvable Temperature Difference (MRTD)

Test Pattern in Target Module

38
SPATIAL FREQUENCY (cy/cm)

0.2 0.4 0.6 0.8 1.0 1.2 1.4

Figure 8a. Minimum Resolvable Temperature Difference (MRTD)

versus Spatial Frequency at Various Background

Temperatures T of System A (S=2)

SPATIAL FREQUENCY (cy/cm)

0.2 0.4 0.6 0.8 1.0 1.2 1.4

Figure 8b. Minimum Resolvable Temperature Difference (MRTD)

versus Spatial Frequency at Various Background

Temperatures T of System B (S=5)

39
SPATIAL FREQUENCY (cy/cm)

Figure 8c. Minimum Resolvable Temperature Difference (MRTD)

versus Spatial Frequency at Various Background

Temperatures T of System C (S=10)

SPATIAL FREQUENCY (cy/cm)

Figure 8d. Minimum Resolvable Temperature Difference (MRTD)

versus Spatial Frequency at Various Background

Temperatures T of System D

40
MRTD

(°C)

SPATIAL FREQUENCY (cy/mrad)

Figure 8e. Minimum Resolvable Temperature Difference (MRTD)

versus Spatial Frequency of Systems A, B, C, D,

E (Blackground Temperature T ^23°C)

and

41
Figure 9a. Minimum Resolvable Temperature Difference (MRTD)

versus Background Temperature of System A (S=2)

for the Two ASHRAE Specified Test Frequencies

Figure 9b. Minimum Resolvable Temperature Difference (MRTD)

versus Background Temperature of System B (S=5)

for the Two ASHRAE Specified Test Frequencies

42
Figure 9c. Minimum Resolvable Temperature Difference (MRTD)

versus Background Temperature of System C (S=10)

for the Two ASHRAE Specified Test Frequencies

Figure 9d. Minimum Resolvable Temperature Difference (MRTD)

versus Background Temperature of System D

for the Two ASHRAE Specified Test Frequencies

43
Figure 10. Image Display of System C for Pattern #4 at

Background Temperature of -17°C

44
4 ASHRAE STANDARDS

o SYSTEM A (S=10)

• SYSTEM A ( S=2

)

^ SYSTEM D

Figure 11a. Factor of Decrease for the Instrument Sensitivity

Versus Object Temperature of Systems A and D

(Using 30°C as Reference)

OBJECT TEMPERATURE (°C)

c ASHRAE STANDARDS

• SYSTEM B ( S=5

)

^ SYSTEM C (S=10)

Figure lib. Factor of Decrease for the Instrument Sensitivity

Versus Object Temperature of Systems B and C

(Using 30°C as Reference)

45
Figure 12a. Absolute Temperature Calibration Curves of System A

at Various Background Temperatures T

(S=2, Aperture = f/1.8)

OBJECT TEMPERATURE (”0

Figure 12b. Absolute Temperature Calibration Curves of System B

at Various Background Temperatures T

(S=2, Aperture = f/1.8)

46
Figure 12c, Absolute Temperature Calibration Curves of System C

at Various Background Temperatures T (S=10)

Figure 13a» Differential Temperature Calibration Curves of

System A at Various Background Temperatures T

( S = 2)

47
TEMPERATURE DIFFERENCE (°C)

Figure 13b. Differential Temperature Calibration Curves of

System B at Various Background Temperatures T

( S = 2)

TEMPERATURE DIFFERENCE (°C)

Figure 13c. Differential Temperature Calibration Curves of

System C at Various Background Temperatures T

(S=10)

48
System with Eyepiece Display

Figure 14,

System with Remote Monitor Display

Instrumentation Setup for Signal Transfer Function

(SiTF) Tests

49
Figure 15a. Relative Brightness versus Temperature Difference

from SiTF Test of System A at Constant Thermal

Level (TL=26.5) for Various Gains

TEMPERATURE DIFFERENCE ("O

Figure 15b. Relative Brightness versus Temperature Difference

from SiTF Test of System B at Constant Thermal

Level (TL=54) for Various Gains

50
RELATIVE

BRIGHTNESS

TEMPERATURE DIFFERENCE (°C)

Figure 15c. Relative Brightness versus Temperature Difference

from SiTF Test of System D at Maximum Thermal

Level (Brightness) for two gains (Contrast)

51
Figure 15d. Relative Brightness versus Temperature Difference

from SiTF Test of System A at Constant Gain (S=2)

for Various Thermal Levels

TEMPERATURE DIFFERENCE (°C)

Figure 15e. Relative Brightness versus Temperature Difference

from SiTF Test of System B at Constant Gain (S=5)

for Various Thermal Levels

52
Figure 16a, Line Spread Function (LSF) of System A as

a Function of Distance in Object Space

(S=2, TL=26, and AT=18oc)

OBJECT SPACE DISTANCE (mrad)

Figure 16b. Line Spread Function (LSF) of System B as

a Function of Distance in Object Space

(S=2, TL=54, and AT=15°C)

53
Figure 17a, Modulation Transfer Function (MTF) of System A as

a Function of Object Space Frequency

(S = 2, TL = 26 , and aT = 180C)

Figure 17h. Modulation Transfer Function (MTF) of System B as

a Function of Object Space Frequency

(S=2, TL=54, and AT=15°C)

54
APPENDIX

Material to be Built (or Modified) by NBS Machine Shop

This section includes detailed drawings of the components that

are required to be constructed in-house by NBS, Figures A-1 to

A-4 illustrate the Target Concept of Target Backgroung Plate with

temperature probe holder. Target Pattern Holder, and Target

Support Plate (items 7, 8, and 3 in figures 2 and 3). Figures A5 to A-13 describe the Sliding Pattern Bracket and Seven Target

Plates. Figures A-14 and A-15 give dimensions of the Target

Source Table and the S e n s o r / M o n i t o r Table (items 1 and 9 in

figures 2 and 3). Figures A-16 and A-17 are drawings of the

Sensor/Monitor Mounting Plate and the Optical Rail (items 11 and

14 in figures 2 and 3), The Optical Rail is currently available

in NBS and need to be modified according to the descriptions.

Figure A-18 is the Coupling Lens Holder. Figures A-19 and A-20

are the Source Mounting Block and the Sensor Mounting Block (item

4 and 12 in figures 2 and 3) which are rectangular blocks of wood

cut to the desired heights for the Blackbody and various sensors.

Figure A-21 gives the dimensions of the Remote Monitor Display

Mounting Block and Mounting Plate (items 21 and 23 in figure 3)

which are built to mount the Display Rotating Table (item 22 in

figure 3), The Rotating Table is an existing item in NBS.

A-1
Target

Background

Plate

a.

<uoAo

0)bC

CO H1 <c

0)

S-i 3

bD

•rH

pK4

A-2

Target

Support

Plate
4

'

Side-view

(not to sc£

Rear view

(On inside, we

need some type

of spring clip

to hold slide

against back of

large plate.)

Figure A-2a. Target Blackground Plate

A-3
y.-20 TAPPED

V

Figure A-2b. Target Temperature Probe Holder

A-4
Ball Detent Looking Down on Slide Holder Top1.' Drill all the way through

3.

Tap hole in step 2 to

allow screw to hold

retainer spring.

increase this

t

Ball

4.

This may require adding

additional material to

top

.

5.

See side view concept.

Figure A-3 . Close-Up of Ball Detent

A-5
(all

holes:

1/4

0) fH -a r. 0) 00 QJ CO c •a u

o J-l CO CO OJ •H CN OJ X CU •H CJO CM c •H

1 )-l 0 1—

1

X

CC3 u CO CO • '<r CO JJ • • •H M 4-1 3 0) 0) CO •H

OJ TJ XJ M c

V-I CO CO o M OJ

1 CJ o rX o cn <r CO x: Cu D. -H CM D

OJ

o ^

1 1

A-6

Figure

A-4.

Target

Support

Plate

1"

Thickness
\h<r i.. I ‘r , A..rr

A.. ^ t ^' \ r

A..

kf

A..

^IC--

A..( 0 7>x _ 'L NV

ll - \K - - A _ %KK

A_

K:-

A-7

figure A

5.

Sliding

Pattern

Bracket

(Front

View)
ASoH

0)60 =

-O OO

<U \= ASC \ 3 ^ to

<U =

60

X

t3 I—I

QJ

n-l on = AS /'~S C U 3 03

r-H CO 4J3

03O

01 03 60 = X T3 00 4-1 0) ^

r-< in = AS

<!• 3 AS \ 3 3

1—( CO 3

CO

03 03 60 = r—(

"Q 00 o

0)

15 - AS 3 ^ 5 3 3 O

CO CO3

<u -

CO3

60

O

X 1-H

03 \ <u

,-1 on 60 •3 = AS 01 <t 3 — 3 ^ « 1/4"

0) - W)^

03

—, = A!

<1-

C33

0) 3: U z

(D AS 33

m 3 3 • 3 3 uo

•rA 3 3 0

}-i 4c

03 = 3 - 60 \0 ~ 3

33 ^ to 140

03 3 • 0

r-4 CO 15

m

X

CJ

CO w

A-8

Figure

A-6*

Sliding

Pattern

Bracket

(Rear

View)
0.7C

A-9
039

-?•

—^ \<r-

/fi V

CSs1^C

<0u

<s

<>»s

STa

VO

CJ

HImI cnMo

^4 uu

(U

4-1 c

OJ CJo3m>cou

flCO

CO

CDC

CJ •H

x:H

ooIII CM

<U 4J

Cfl

OhCu0)

4.) CC

P-i

OJW)M

«0 H

CX5I <J

cu

)-l 3

ao •H

A-10
0.z^

—>i K

^

A-11
iro

A-12

Front

View

Top

View

of

Center

Cross-section
0.16

A-13

Figure

A-11.

Target

Pattern

Plate

^5

1/16"

Thickness
A-14

Figure

A-12.

Target

Pattern

Plate

#6

1/8"

Thickness
A-15

I'lonL

View

Top

View

of

Center

Cross-section
1. Angle iron solid construction of frame.

2. Cover with thin sheet metal stock. (Paint to suit.)

(Not shown here.)

3. Center plate on top must support solid 200-300 lbs.

Qi” thick aluminum or steel, hole spacings to fit model

2501 jactuator)

4. Hole spacings on bottom corners to fit model

4-30-113P-2 casters. (2 with brakes, 2 without)

<: 2 /^ ^

Figure A-14. Source Table

A-16
1. Angle iron solid construction of frame.

2. Cover with thin sheet metal stock. (Paint to suit.)

(Not shown here.)

3. Center plate on top must support 500 lbs.

(3/4” thick aluminum or steel)

4. Hole spacings on bottom corners to fit model

4-30-1 13P-2 casters. (2 with brakes, 2 without)

<

Figure A-15. S enso r / Mo n i t o r Table

A-17
4 o/</es

C^' UU</MU.4^

bf^iCK anocf/^ec!

Figure A-16. Sensor /Monitor Mounting Plate
A-1 9
ir

thick alunwnum

4- HOLES TAPPED Z - b<o /\6

Figure A-18, Coupling Lens Holder

A-20
Figure A-20. Sensor Mounting Block

A-21
o

Figure A-21. Remote Monitor Display Mounting Plate and Block

A-22
rO«M Nas-I 1 4A (REV 1 1 84)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1 . PUBLICATION OR

REPORT NO,

NBSIR 85-3131

2. Performing Organ. Report No. 3. PubI ication Date

June 1985

4. TITLE AND SUBTITLE

Laboratory Design and Test Procedures for Quantitative Evaluation

of Infrared Sensors to Assess Thermal Anomalies

5. AUTHOR(S)

Y. May Chang, Richard A. Grot and James T. Wood

6. PERFORMING ORGANIZATION (If joint or other than NBS, see in struction s)

NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COAAMERCE

GAITHERSBURG, MD 20899

7. Contract/Grant Np. Interagency Agreement

DEAI-01-76

8. Type of Report & Period Covered

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City. State. ZIP)

Office of Building Energy Research and Development

U.S. Department of Energy

Washington, DC 20585

10. supplementary notes

l~ I Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or literature survey, mention it here)

This report presents the description of the laboratory apparatus and preliminary results

of the quantitative evaluation of three high-resolution and two low-resolution infrared

imaging systems. These systems which are commonly used for building diagnostics are tested under various background temperatures (from -20 °C to 25 °C) for their minimum

resolvable temperature differences (MRTD) at spatial frequencies from 0.03 to 0.25

cycles per milliradian. The calibration curves of absolute and differential temperature

measurements are obtained for three systems. The signal transfer function and line

spread function at ambient temperature of another three systems are also measured.

Comparisons of the dependence of the MRTD on background temperatures from the measured

data with the predicted values given in ASHRAE Standards 101-83 are also included. The

dependence of background temperatures for' absolute temperature measurements are presented, as well as comparison of measured data and data given by the manufacturer.

Horizontal on-axis magnification factors of the geometric transfer function of two

systems are also established to calibrate the horizontal axis for the measured line

spread function to obtain the modulation transfer function. The variation of the

uniformity for horizontal display of these two sensors are also observed. Included are detailed descriptions of laboratory design, equipment setup, and evaluation procedures

of each test.

1^2. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by je-,co on Background temperature; calibration curves; display uniformity; infrared sensing systepvj

laboratory evaluation; line spread function; magnification factor; minimum resolvable ' temperature difference; modulation transfer function; signal transfer function; spatial

'13. AVAILABILITY frequency; target tempefACurs

I^^Unl imited

I

I For Official Distribution, Do Not Release to NTIS

Superintendent of Documents, U.S. Government Printing Office, Washington, DC

[XXOrder From National Technical Information Service (NTIS), Springfield. VA 22161

14. NO. OF

PRINTED PAG;

8

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