NVThermIP vs TOD: matching the target acquisition range criteria

Abstract

Currently, three major approaches exist to predict Target Acquisition (TA) performance with thermal imagers: i) the TOD laboratory method and model, ii) the NVThermIP model and iii) the MTDP lab method and TRM3 model. In this study, TOD measurements, TOD predictions and NVThermIP predictions are compared for a number of simulated sensors ranging from very well-sampled to highly under-sampled. A similar comparison study using a previous (2001) version of the NVTherm model showed huge differences in sensor performance predictions SPIE Proceedings Vol. 4719, 51-62;2002). The most important result of the current study is that NVThermIP predictions are much closer to the TOD measurements and predictions than those of its predecessor, showing limited effect of under-sampling. Quantitatively, TA range predictions for well-sampled imagers are equivalent and NVThermIP predicts 25% longer ranges than the TOD model for under-sampled imagers with M P = 0.35· V P and β = 1.25, where V P are the criteria published with NVThermIP to predict TA range for a variety of target sets, M P are the corresponding TOD magnification factors, and β is the slope of the probability vs range function in the TOD target acquisition model. Which method yields the best predictions under which circumstances should be the subject of an empirical study using TA performance for real targets. It is therefore advised that all available TA validation data be presented in such a way that all models and methods can be compared to the data directly and unambiguously.

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

“…For example, the ratio is around 1.27 for a typically under-sampled imager (sensor 1 and 2). This is in agreement with the earlier finding 13 that NVThermIP is about 25% more optimistic for under-sampled imagers than TOD compared to well-sampled imagers.…”

“…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. While the TOD essentially remained unchanged over the years, the TTP metric has undergone major changes.…”

“…Probability versus range relationship P(r) is calculated with the following two equations 6,13 : where r 75 is the target acquisition range (in km) at probability P = 0.75, β determines the slope of the relationship and has value β =1.25 in our model 6,13 , A is the target set characteristic size (in m, see section A.2), C 0 is the target set characteristic inherent RSS contrast (ΔT 0 for thermal, see section A.2), and S C0 (= VA -1 in the high contrast limit) is the corresponding triangle threshold size (triangle square-root area in mrad) from the TOD curve. Finally, M 75 is a magnification factor between required target and triangle size that quantifies the task difficulty (see section A.2).…”

“…For each sensor, optimum viewing distance was chosen. Using the procedure described elsewhere 13 , the range calculations are calculated back to target size on the Focal Plane Array. V 50 was chosen in such a way that for the sensor with the highest Fλ/d value (the most wellsampled sensor), predicted triangle size matched that of the TOD measurements.…”

“…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 .…”