WHAT ABOUT ADIABATIC NORMAL MODES?
In this paper we closely examine the performance of several propagation models, i.e., KRAKEN (coupled and adiabatic) and PE (energy-conserving), applied to a number of the SWAM'99 range-dependent shallow water test cases (FLAT, DOWN, and UP). We begin by considering range-independent behavior (including the ORCA model) in: the CAL case of Workshop'97 (Vancouver, '97),9 the first segment of FLATa, and the Benchmark Wedge test case3 but with a flat bottom of 200 m depth. We next examine the proper Benchmark Wedge behavior for the sloping bottom for our PE (conserving and nonconserving) and for our normal mode model (KRAKEN, adiabatic and coupled). These preliminary tests confirm that the models are behaving properly under known conditions and that the input parameters have been appropriately set. Thus, when we study the models' behavior on the new SWAM'99 cases we will have some confidence that they are being applied properly. It is nontrivial to run these models even when one is familiar with them. The SWAM'99 test cases which are examined here are run only to 10 km range (five-step segments) and at a single frequency of 25 Hz. No elasticity is considered. We find that all the models generally agree, but there are quantitive differences. Since there are no proper benchmark solutions for these SWAM'99 test cases, it is difficult to determine to what extent any of them are in error. However, for the purposes of Matched Field Processing, particularly the tomographic geoacoustic inversion using adibatic normal modes (KRAKEN), it is likely that the simple adiabatic normal mode KRAKEN model is sufficiently accurate under most circumstances, i.e., unless there is a loss or gain of a critical mode.