An interesting paper by C. Silva, T. A. DelValls and M.L. Martín-Díaz titled "Environmental monitoring and mapping in a tidal salt marsh creek affected by fish aquaculture using Worldview-2 multispectral imagery" describes a means for calculating bathymetry from 2 of the 8 spectral bands from DigitalGlobe's WorldView 2 satellite. I wonder if we could do the same thing from balloons and kites?

3.5. Determination of bathymetry: The bathymetry is derived from the multispectral image by applying the ratio method (Stumpf et al., 2003) using the Y/CB bands. The first step to derive bathymetry from the image is to determine relative bathymetry using the natural log transform of the reflectance values.

http://www.digitalglobe.com/downloads/8bc/Draft-Worldview-RioSanPedro_2010-11-22_claudiosilva.pdf