Targets

Targets are modules needed to generate images of reference image patterns needed for systems for testing imaging EO systems.    INFRAMET manufactures a long series  of targers that can be divided  divides test targets according to intended main application into three main groups:

  1. targets for testing thermal imagers operating at MWIR/LWIR spectral bands (called later Infrared targets),
  2. targets for testing imagers  sensitive in VIS-SWIR spectral band (called later Visible targets),
  3. targets for testing fused imagers sensitive in both MWIR-LWIR  band and VIS-SWIR band (called later Fused targets).

Targets manufactured by Inframet are typically intended for use in test systems manufactured by the same company and are rarely sold as independed units. Therefore this section should be treated not as typical commercial offer but as a review od technologies that can be used to manufacture test systems  presented in  Test System section.

a) b) c)

Image of IR target
recorded by tested thermal imager

Image of Visible target
recorded by tested VIS-NIR camera

Image of fused target
recorded by tested fused imager


IR TARGETS

IR targets for testing infrared imaging systems (thermal imagers) are manufactured by creating precision holes in metal sheets of different shapes. When a blackbody is put behind such a target, the tested thermal camera sees a "target" of shape determined by the holes on an uniform background. The apparent temperature of this "target" is equal to blackbody temperature. Our DT/MS systems for testing thermal imagers use a series of small size (54 mm diameter) targets fixed to MRW-8 rotary wheel. Bigger size IR targets are used by LAFT test systems but these big targets are excluded from this section.


Fig. 2. Photo of two 4-bar targets

INFRAMET offers fourteen different types of standard IR targets:

Attention:

Diameter of the active area (area covered with high emissivity coating) of standard Inframet targets is equal to 54 mm. Mechanical dimensions of the Inframet target plates are set to fit to counterbores in the standard MRW-8 rotary wheel. However, Inframet can manufacture targets plates that can fit to rotary wheels (or blackbody target support plates) offered by any manufacturer.

Spatial frequency of 4-bar targets is calculated using the formula

where n is the spatial frequency of the 4-bar target of bar width equals a when the target is used with IR collimator of focal length f’. Angular size of triangle, circular targets, slit targets, and square targets is calculated as

where a is the angular size of the target of linear size d when the target is used with IR collimator of focal length f’.

4-BAR TARGETS

These targets (4-bar, 7:1 ratio, single pattern) are used to perform Minimum Resolvable Temperature Difference (MRTD) measurements. A set of targets with various spatial frequencies is used to measure MRTD as a function of spatial frequency. Targets of different bars size (spatial frequency) are fixed to the rotary wheel.

Tab.1. Spatial frequencies of standard 4-bar targets for collimators of different focal lengths

bar width [mm] spatial frequency [lp/mrad]
  f'=0.6m f'=0.77m f'=1m f'=1.2m f'=1.5m f'=1.6m f'=2m f'=2.5m f'=3 m
5 0,06 0,08 0,1 0,12 0,15 0,16 0,2 0,25 0,3
4 0,08 0,1 0,13 0,15 0,19 0,20 0,25 0,31 0,38
3,36 0,09 0,11 0,15 0,18 0,22 0,24 0,3 0,37 0,45
2,83 0,11 0,14 0,18 0,21 0,27 0,28 0,35 0,44 0,53
2,38 0,13 0,16 0,21 0,25 0,32 0,34 0,42 0,53 0,63
2 0,15 0,19 0,25 0,3 0,38 0,40 0,5 0,63 0,75
1,68 0,18 0,23 0,3 0,36 0,45 0,48 0,6 0,74 0,89
1,41 0,21 0,27 0,35 0,43 0,53 0,57 0,71 0,89 1,06
1,19 0,25 0,32 0,42 0,5 0,63 0,67 0,84 1,05 1,26
1 0,3 0,39 0,5 0,6 0,75 0,80 1 1,25 1,5
0,84 0,36 0,46 0,6 0,71 0,89 0,95 1,19 1,49 1,79
0,71 0,42 0,54 0,7 0,85 1,06 1,13 1,41 1,76 2,11
0,59 0,51 0,65 0,85 1,02 1,27 1,36 1,69 2,12 2,54
0,5 0,6 0,77 1 1,2 1,5 1,60 2 2,5 3
0,42 0,71 0,92 1,19 1,43 1,79 1,90 2,38 2,98 3,57
0,35 0,86 1,1 1,43 1,71 2,14 2,29 2,86 3,57 4,29
0,3 1 1,28 1,67 2 2,5 2,67 3,33 4,17 5
0,25 1,2 1,54 2 2,4 3 3,20 4 5 6
0,21 1,43 1,83 2,38 2,86 3,57 3,81 4,76 5,95 7,14
0,18 1,67 2,14 2,78 3,33 4,17 4,44 5,56 6,94 8,33
0,15 2 2,57 3,33 4 5 5,33 6,67 8,33 10
0,12 2,5 3,21 4,17 5 6,25 6,67 8,33 10,42 12,5
0,1 3 3,85 5 6 7,5 8,00 10 12,5 15
0,08 3,75 4,81 6,25 7,5 9,38 10,00 12,5 15,63 18,75
0,06 5 6,42 8,33 10 12,5 13,33 16,67 20,83 25
0,05 6 7,7 10 12 15 16,00 20 25 30

Attention:

4-bar targets of spatial frequencies not included in the table are available upon specific request.

TRIANGLE TARGETS

Triangle target are needed for testing thermal imagers using TOD (Triangle Orientation Discrimination) method. TOD is an alternative to MRTD measurement or MDTD. TOD method has a number of theoretical and practical advantages over MRTD or MDTD.

Tab.2. List of standard triangle targets

Angular size [mrad]
triangle edge [mm] f'=0.6m f'=0.77m f'=1m f'=1.2m f'=1.5m f'=1.6m f'=2m f'=2.5m f'=3 m
20 33,33 25,97 20 16,67 13,33 12,5 10 8 6,67
10 16,67 12,99 10 8,33 6,67 6,25 5 4 3,33
5 8,33 6,49 5 4,17 3,33 3,13 2,5 2 1,67
2,5 4,17 3,25 2,5 2,08 1,67 1,56 1,25 1 0,83
1,25 2,08 1,62 1,25 1,04 0,83 0,78 0,63 0,5 0,42
1 1,67 1,3 1 0,83 0,67 0,63 0,5 0,4 0,33
0,75 1,25 0,97 0,75 0,63 0,5 0,47 0,38 0,3 0,25
0,5 0,83 0,65 0,5 0,42 0,33 0,31 0,25 0,2 0,17
0,25 0,42 0,32 0,25 0,21 0,17 0,16 0,13 0,1 0,08

Attention:

Other sizes are available upon specific request.

PINHOLE TARGETS

Pinhole targets are needed for measurement of Minimum Detectable Temperature Difference (MDTD) function, and during alignment or and bore-sight process.

Tab.3. List of standard pinhole (circular) targets

Angular size [mrad]
Diameter [mm] f'=0.6m f'=0.77m f'=1m f'=1.2m f'=1.5m f'=1.6m f'=2m f'=2.5m f'=3 m
25,6 42,67 33,25 25,6 21,33 17,07 16 12,8 10,24 8,53
12,8 21,33 16,62 12,8 10,67 8,53 8 6,4 5,12 4,27
6,4 10,67 8,31 6,4 5,33 4,27 4 3,2 2,56 2,13
3,2 5,33 4,16 3,2 2,67 2,13 2 1,6 1,28 1,07
1,6 2,67 2,08 1,6 1,33 1,07 1 0,8 0,64 0,53
0,8 1,33 1,04 0,8 0,67 0,53 0,5 0,4 0,32 0,27
0,4 0,67 0,52 0,4 0,33 0,27 0,25 0,2 0,16 0,13
0,2 0,33 0,26 0,2 0,17 0,13 0,13 0,1 0,08 0,07
0,1 0,17 0,13 0,1 0,08 0,07 0,06 0,05 0,04 0,03
0,05 0,08 0,06 0,05 0,04 0,03 0,03 0,03 0,02 0,02

Attention:

Other sizes are available upon specific request.

SQUARE TARGETS

Square targets (widow targets) are needed for measurements of Noise Equivalent Temperature Difference (NETD), Fixed Pattern Noise (FPN), Signal Transfer Function (SiTF), Aperiodic Transfer Function (ATF), Minimum Detectable Temperature (MDT).

Tab.4. List of standard square targets

Square side [mm]
Diameter [mm] f'=0.6m f'=0.77m f'=1m f'=1.2m f'=1.5m f'=1.6m f'=2m f'=2.5m f'=3 m
25,6 42,67 33,25 25,6 21,33 17,07 16 12,8 10,24 8,53
12,8 21,33 16,62 12,8 10,67 8,53 8 6,4 5,12 4,27
6,4 10,67 8,31 6,4 5,33 4,27 4 3,2 2,56 2,13
3,2 5,33 4,16 3,2 2,67 2,13 2 1,6 1,28 1,07
1,6 2,67 2,08 1,6 1,33 1,07 1 0,8 0,64 0,53

Attention:

Other sizes are available upon specific request.

SLIT TARGETS

Slit targets are manufactured by cutting holes in shape of a rectangle of different width. These targets are needed during measurement of SRF (slit response function).

Tab.5. Slit targets

Slit width [mm]
Diameter [mm] f'=0.6m f'=0.77m f'=1m f'=1.2m f'=1.5m f'=1.6m f'=2m f'=2.5m f'=3 m
15 0,02 0,026 0,033 0,04 0,05 0,05 0,067 0,083 0,1
10 0,03 0,039 0,05 0,06 0,075 0,075 0,1 0,125 0,15
7,1 0,042 0,054 0,07 0,085 0,106 0,106 0,141 0,176 0,211
5 0,06 0,077 0,1 0,12 0,15 0,15 0,2 0,25 0,3
3,5 0,086 0,11 0,143 0,171 0,214 0,214 0,286 0,357 0,429
2,5 0,12 0,154 0,2 0,24 0,3 0,3 0,4 0,5 0,6
1,8 0,167 0,214 0,278 0,333 0,417 0,417 0,556 0,694 0,833
1,25 0,24 0,308 0,4 0,48 0,6 0,6 0,8 1 1,2
0,84 0,357 0,458 0,595 0,714 0,893 0,893 1,19 1,488 1,786
0,59 0,508 0,653 0,847 1,017 1,271 1,271 1,695 2,119 2,542
0,42 0,714 0,917 1,19 1,429 1,786 1,786 2,381 2,976 3,571

Attention:

Other sizes are available upon specific request.

EDGE TARGETS

Edge targets are useful for indirect measurement of Modulation Transfer Function (MTF) on the basis of measured directly Edge Spread Function (ESF). The are manufactured by cutting a half-moon of sharp smooth edge.

Contact INFRAMET for further details.

ALIGNMENT TARGETS

Alignment targets are useful for boresighting, focusing and alignment applications. The targets are manufactured by cutting pinhole-and-cross combinations. Contact INFRAMET for further details.

DOUBLE 4-BAR TARGETS

These targets are useful when it is necessary to measure MRTD function for both vertical and horizontal orientation of the bars. It is possible to shorten significantly measurement time.

Contact INFRAMET for further details.

MULTIPLE 4-BAR TARGETS

These targets are cost-effective solution for MRTD measurements. A single multiply 4-bar target with several 4-bar patterns can replace a few 4-bar targets with a single pattern.

Attention: Application of these targets can decrease measurement accuracy. Please contact Inframet for recommendations.

MULTIPLY PINHOLE TARGETS

These targets are cost-effective solution for MDTD measurements. A single multiply pinhole target with several pinhole patterns can replace a few pinhole targets with a single pattern.

Attention: Application of these targets can decrease measurement accuracy. Please contact Inframet for recommendations.

ABINGDON CROSS TARGETS

These targets are used to evaluate the effectiveness of image processing algorithms in presence of noise. Contact INFRAMET for further details.

DISTORTION TARGETS

These targets are used to evaluate distortion of the image generated by tested thermal imagers. Contact INFRAMET for further details.

GREY SCALE TARGETS

Gray scale targets are used to measure linearity and dynamic range of the tested thermal imagers in a single operation.

Contact INFRAMET for further details.

SILHOUETTE TARGETS

Silhouette targets are used evaluation of recognition ranges of real targets with the tested thermal imager.

Contact INFRAMET for further details.

VISIBLE TARGETS

Visible targets can be divided onto two main groups: A)reflective targets, B)transmissive targets. Targets from the first group are mainly low cost targets manufactured by printing black pattern on highly reflective substrate (white paper). Targets from the second group are mostly manufactured by creating non-transparent (or semi-transparent) coating pattern on transparent substrate (or inverse situation). Method A does not enable creation of highly precision patterns and can be used only to manufacture big targets to be used for simplified evaluation of visible imaging systems. This method is not used by Inframet that prefers method B. The latter method enables development of visible targets with sub-micrometer accuracy. The targets from B group are typically manufactured using photolithography methods by creating chrome pattern on clear glass substrate (positive contrast targets).

 

Fig.1. USAF 1951 target a)photo of target plate, b)target drawing

Visible targets are mostly used as resolution targets. There have been proposed many different types of resolution targets. However, Inframet prefers USAF 1951 target because of its universality (ability to measure resolution of both low resolution and high resolution imagers).

The USAF 1951 targets of 100% contrast are available commercially from many different sources because 100% contrast targets are relatively easy to be manufactured. However, the typical targets of 100% contrast poorly simulate real low contrast targets.

Inframet has mastered technology of variable contrast resolution targets. Inframet test systems (like TVT/MS systems) use a series of USAF 1951 targets having different contrast and therefore make possible measurement of Minimal Resolvable Contract (MRC) function of tested visible/NIR cameras. Inframet can manufacture USAF 1951 targets of contrast from 2% to 100%. Typical contrast values are: 100%, 50%, 30%, 20%, 10%, 5%, 2%. This span of contrasts enables accurate testing and evaluation of visible/NIR cameras.

Table 1. Parameters of USAF 1951 targets manufactured by Inframet

Parameter Value
Pattern type 3-bar
Pattern groups from 0 to 7 (option 0-8)
Spatial frequency range 1-228 lp/mm (option 1-456 lp/mm)
Contrast from 2% to 100% (typically positive targets but negative targets also possible)
Substrate soda lime glass (option quartz)
Pattern coating chromium
Dimensions of target plate 23x23 mm

MULTISPECTRAL TARGETS

These are large size targets offered as direct test systems for testing fused imagers.