## 5aUW3. A numerical investigation of the validity of a ray-based acoustic wave field expansion.

### Session: Friday Morning, December 6

### Time: 8:28

**Author: Michael G. Brown**

**Location: RSMAS-AMP, Univ. of Miami, 4600 Rickenbacker Cswy., Miami, FL 33149**

**Author: Marco Ianniruberto**

**Location: RSMAS-AMP, Univ. of Miami, 4600 Rickenbacker Cswy., Miami, FL 33149**

**Abstract:**

The purpose of the work reported here is to determine the domain of
validity in frequency and range of ray-based acoustic wave field expansions
under typical deep ocean conditions. This is accomplished by comparing transient
wave fields computed using the ray-based MaCh1 propagation model to those
computed using the mode-based SNAP propagation model. Although MaCh1 is
ray-based, it correctly treats caustics of arbitrary complexity. Attention is
confined to range-independent environments so that potential ray theory
deficiencies unrelated to ray chaos can be isolated; the latter problem will be
investigated separately. Both high lattitude (constant gradient) and temperate
(canonical) environments are considered. Two types of errors associated with the
ray-based wave field expansion are identified. These errors may be attributed to
the omission of: (1) complex rays (tunneling phenomena) near the source; and (2)
beam displacement effects for near-grazing rays. Ray-based errors, which are
generally isolated in time, grow with decreasing frequency and increasing range.
Overall, however, the agreement between the ray- and mode-based wave fields is
surprisingly good with, say, f[inf 0]=20 Hz, (Delta)f=25 Hz, r=300 km, or f[inf
0]=80 Hz, (Delta)f=100 Hz, r=1000 km. [Work supported by ONR.]

ASA 132nd meeting - Hawaii, December 1996