medium. Properties of seawater that affect sound speedare salinity, temperature, and pressure. Output from thisprogram is classified and should be labeled as required.PASSIVE ACOUSTIC PROPAGATIONLOSS (PPL)LEARNING OBJECTIVESIdentifyapplications, limitations, and assumptions ofthe PPL program. Interpret PPL outputs.The PPL program calculates transmission loss as afunction of range, frequency, source depth, and receiverdepth. The calculations from this program will be usedin the prediction of ASW sensor systems performance.The purpose of this program is to define the acousticpropagation conditions within the ocean area of interest.It is intended as an interface between environmentaldata read from the ocean environmental file (OEF) andoperational data.The program will translateinformation about existing oceanographic conditionsinto an assessment of PPL versus range that is necessaryfor sensor system performance predictions.APPLICATIONThe PPL program computes the loss of soundintensity in traveling from the selected source (forexample, submarine) to the receiver (for example,passive sonobuoy) for ranges (kyd) out to the maximumrange specified. The operator-selectable input is thedesired frequencies, source and receiver depths, andmaximum range. The propagation-loss curve aids theoperator in computing detection ranges and possibledetection paths.The range should be chosen to include the first CZ.A typical maximum range value varies from 60 to 100kyd.When the propagation-loss curve is displayed on themonitor, the operator can see the transmission lossassociated with each range. In general, the propagationloss increases with range but may decrease rapidly(spike) when environmental conditions allow formationof CZs. If the operator knows the figure of merit(FOM), in decibels (dB), detection ranges can bedetermined instantly by looking at the display. At anyrange point where the FOM is greater than thepropagation loss, the probability of detection (POD) isat least 50 percent.LIMITATIONS AND ASSUMPTIONSThe restrictions as well as the principles taken forgranted in using the PPL program are as follows:l The PPL program incorporates low-frequencybottom-loss (LFBL) data base processes, assumptions,and correction factors. Viability of output depends uponthe degree of difference between the model and actualseabed conditions.. System correction factors are preset to define anomnidirectional/vertical-line array DIFAR (VLAD)sonobuoy.. Maximum range should include the first CZ.l Horizontal homogeneity y is assumed. Therefore,the output should be used with caution in areas of highvariability (for example, fronts and eddies).l The SSP program must be used to create theenvironmental data set used by RAYMODE. The SSPprogram stores a sound speed profile, bottom depth,high- and low-frequency bottom-type information,wind speed, and so on, in the OEF.. Propagation-loss curves may be generated fortarget frequencies in the range of 1 to 35,000 Hz. Dueto the limitations of the LFBL data base, reliable outputis constrained to frequencies >30 Hz.FUNCTIONAL DESCRIPTIONThe RAYMODE propagation-loss model wasdeveloped at the Naval Underwater Systems Center,New London, Corm. The original version of this modelhas been updated to incorporate factors for determiningbottom-loss and system correction factors. This modelconsiders the ocean bottom as a varying sound receptorand not simply a reflector. Computation of losses in thebottom sediment are a feature of PPL that treats thebottom of the ocean as a continuation of the watercolumn, and computes the contribution of the bottomsediment to propagation loss, considering refractedpaths through the sediment and reflections at thebasement.Locations beyond the coverage of the LFBL database use the COLOSSUS data base model to estimatepropagation loss. Output from this program is classifiedand should be labeled as required.8-7