<title>Extensive analysis of low-level IR transmission measurements taken over a 15-km path during EOPACE with IRBLEM</title>

Abstract

Results of over 300far JR and mid JR transmission measurements taken during several EOPACE (BO Propagation Assessment in Coastal Environments) intensive operational periods (lOP's) over the low-level 15 km transmission path across San Diego bay are presented. A thorough comparison with calculations obtained using simultaneously measured bulk meteorological parameters with the IR Boundary Layer Model (IRBLEM), illustrate the effects thatrefractance, aerosol extinction and molecular extinction can have on the transmission. Discrepancies between the transmission measurements and the model's predictions are identified and investigated by varying various model parameters, and looking at available measured aerosol size distributions and refraction measurements over the path. Comparison with the measured transmissions are reasonably good and show that the total transmission depends critically on all three effects, with the molecular transmittance depending upon the water vapour density and the characteristics of the JR source and detector, the aerosol transmittance upon the visibility (aerosol concentration), and the refractive effects on the stability of the marine boundary layer or the virtual potential air-sea temperature difference.

Development of the Mediterranean extinction code (MEDEX)

“…2 The results show that refractive effects are the primary parameter influencing near-surface propagation, while aerosols can also have a very large effect in this coastal region. 3 The electro-optical propagation codes IRBLEM 4 and EOSTAR 5 aim at a description of these effects by including both refraction and extinction due to gases and aerosols for the marine environment. The previously mentioned MODTRAN code describes the attenuation of electro-optical radiation by gases and aerosols.…”

Enhanced IR point target detection by atmospheric effects

“…on the other hand at sea most of the time the air is somewhat cooler than the sea due to evaporation of surface water, which leads to a slightly subrefractive boundary layer, where the air temperature decreases with height according to a logarithmic profile. An example of the magnitude of this effect, calculated with the model IRBLEM [20] for a simple condition with an air temperature (at 10 m) of 14 °C and a water temperature of 15 °C and a relative humidity of 70% (at 10 m). The Air to Sea Temperature Difference (ASTD) is thus -1 °C.…”

“…A major step towards possibly increased IRST performance was created by the wider availability of JR FPA's since the last decade. As can be expected however, the introduction of a sensor, based upon a considerable number of FPA's (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24), takes time, first of all because new, more complex processors have to be built, but secondly because of the cost involved with the EPA's and the relatively small, mainly military market. Various concepts have been described, such as the Staring Jnfrared Passive Sensor (SJRPS, USA) [3], a German technology demonstrator [4], and the EUCLID RTP8.2 CUPOLA concept [5].…”

TG16 point target detection experiment POLLEX, Livorno 2001

“…SHIPIR model [1] ) and one on the modelling of sensors for detection and tracking of low flying targets at sea ( eg. IRTool [2], IRBLEM [3] and LWKD [4] models ). The cooperation includes experimental work for validation of the models.…”