TOD, NVTherm, and TRM3 model calculations: a comparison

Abstract

At the moment there are three potential models and associated measures to replace the FLIR92 model and the MRTD as the standard for sensor performance characterization and TA range predictions. These are: 1) the NVTherm model that calculates the MRTD-ID, 2) the TRM3 model that calculates the MTDP and 3) the TOD model that calculates the TOD. The three models are grossly different in theoretical approach. We ran the models for the same set of hypothetical cameras. As default sensor, we used a 'typical' under-sampled Focal Plane Array camera. Then, we independently varied the pre-and post-filter MTF's over a wide range while keeping the sampling frequency fixed so that the cameras ranged between well-sampled and highly undersampled. The differences in outcome are striking. For example, for a range of sensors around the default the TOD model predicts that performance is determined primarily by the sampling frequency, while NVTherm predicts that pre-an post-filter blur dominate in this region. The results with TRM3 are surprising: the model predicts that increasing image information content by applying microscan to the default sensor, decreases predicted TA performance. The origin lies in the use of the periodic four-bar test pattern and the definition of the MTDP. In the low contrast region, the MTDP and the TOD are similar but the MRTD-ID deviates from these two. The MTDP and MRTD-ID are different even in the well-sampled region where they both should be equivalent to the conventional MRTD. The study shows that the choice of a model has a large impact on sensor design decisions or trade-offs between sensors. The TOD method is the most general of the three approaches and has the strongest basis. Until now, validation of the model predictions is very limited. Therefore, a joint TA performance study with simulated sensors (e.g. those used in the present study) and target contrast as variables would be very useful.

Target acquisition performance: effects of target aspect angle, dynamic imaging, and signal processing

“…TA models [9][10][11][12][13][14][15][16] such as the TOD model, NVThermIP and TRM3 need to be extended and validated for these largely different target sets, sensor properties, image dynamics and processing techniques, but currently the amount of empirical data is limited and often only addresses one of the above-mentioned differences at the same time. For instance, a large effort of the US research laboratory is directed towards extension of the current models for different target sets such as small arms 17,18 , clothing 19 , paramilitary and civilian vehicles 20 , small boats 21 , or even faces 22 in different spectral regions.…”

Visual acuity and contrast sensitivity with compressed motion video

“…to incorporate signal processing effects. A quantitative comparison between TOD and TTP in 2002 40 showed huge differences. With the newer version 36 the TTP predictions are closer to the TOD although the models still weigh the effects of under-sampling differently 41 .…”

“…TRM3 is the TA range model associated with the MTDP, and the model is available as a mature software package. A comparison with the two other approaches has been made in 2002 40 and the model has not changed since. The laboratory test can easily be performed with a standard MRTD setup but suffers from the same well-known MRTD observer bias problems which have been overcome with the TOD method.…”

Sensor performance as a function of sampling (d) and optical blur (Fλ)

“…They all claim to cope with well-sampled and under-sampled imagers, but they disagree in the relative importance of detector spacing and diffraction blur on the 'effective resolution' or VA with the sensor. In addition, they behave differently in the transition region 12,13 . For example, a quantitative comparison between TOD and TTP (the model underlying the NVTherm thermal imager range prediction model) in 2002 showed huge differences 12 .…”

“…In addition, they behave differently in the transition region 12,13 . For example, a quantitative comparison between TOD and TTP (the model underlying the NVTherm thermal imager range prediction model) in 2002 showed huge differences 12 . Predictions with an updated version of the TTP metric (the basis of the NVThermIP model) are much closer to the TOD 13 : when the performance with blur-limited sensors is set equal, NVThermIP is about 25% more optimistic in range performance prediction for under-sampled imagers than the TOD is.…”