Tomographic measurements directly probe the existence and nature of signals at the lowest wavenumbers. These data are also sensitive to variability almost to the ocean bottom, and thus can detect changes below the depths at which XBT and float data are obtained. The impact of the integral measurements on the quality of ocean estimation using numerical models remains an open question, however. At this time, greater coverage of the world's oceans by acoustic tomography can be implemented at an annual cost that is no greater than other observational approaches. The major costs of tomography are the initial capital costs of the instrumentation and its installation.
Efforts are currently under way to reduce the costs of sources and receivers.
Once the instruments have been installed, however, the operational costs to make continuing measurements are low. The amortized cost of the technique is therefore attractive, even using present-day source and receiver technology. Marine Mammals and Acoustic Tomography. No species vacated the areas around the sound sources during transmissions. The MMRP investigators concluded that these subtle effects would not adversely impact the survival of an individual whale or the status of the North Pacific marine mammal populations.