## 3pAO5. The bidirectional reflectance distribution function of an ocean ridge.

### Session: Wednesday Afternoon, December 4

### Time: 3:05

**Author: Nicholas C. Makris**

**Location: Naval Res. Lab., Washington, DC 20375**

**Author: Laurie T. Fialkowski**

**Location: Naval Res. Lab., Washington, DC 20375**

**Abstract:**

The bidirectional reflectance distribution function (BRDF) of a typical
highly lineated deep-ocean ridge on the western flank of the Mid-Atlantic Ridge
is estimated by applying classical radiometric theory to long-range bistatic
reverberation measurements obtained during the ARSRP Main Acoustics Experiment
of 1993. The BRDF of a surface is defined as the ratio of the reflected radiance
toward the direction of the receiver to the irradiance in the direction toward
the source. Therefore, such effects as two-way transmission loss, the areal
resolution of the measurement, and its foreshortening are accounted for in
computation of the BRDF. (For example, the BRDF for a Lambertian surface is
simply 1/(pi).) In particular, high-resolution bathymetry of 5-m resolution,
roughly the scale of the acoustic wavelength for the low-frequency measurements,
is used to determine surface orientation and foreshortening. The parabolic
equation is used to compute two-way transmission; a ray trace is used to
determine incident and scattered angles at the surface; and a spatial
convolution is used to account for the spatially varying areal resolution of the
measurement system. Statistical fluctuations due to nonlinear speckle noise
inherent in the measurements are reduced by stationary averaging and are
stabilized by logarithmic transformation.

ASA 132nd meeting - Hawaii, December 1996