Wednesday 30 October 2013

Frogs and leaf growth

Back in January I noted research by into infrared reflectance of insects carried out by Michael Mielewczik and others. Michael has contacted me again about two more papers on similar subjects.

The first is Non-Invasive Measurement of Frog Skin Reflectivity in High Spatial Resolution Using a Dual Hyperspectral Approach [1] (on PLOS ONE here with a PDF here).

As before, the team used a camera with filtering that split near-infrared (specifically the red-edge between 675-775 nm) and blue to explore the 'colour' of frog skin. They also used a two further hyperspectral cameras sensitive to visible and near-infrared between 400 and 1000 nm and to SWIR (short wave infrared) between 1000 and 2500 nm. This image is of agalychnis callidryas using the red-edge camera.

I've come across hyperspectral cameras before and they're quite fascinating devices. They produce a multi-dimensional image where each of the pixels in the x and y plane have a complete spectrum recorded in the z axis ... so z records intensity at a range of wavelengths. This means that you can choose which wavelength (or wavelengths) to view the scene after the fact. This multiplies the amount of data dramatically of course.

The second paper uses infrared imaging to help a study of leaf growth. The paper is Diel leaf growth of soybean: a novel method to analyze two-dimensional leaf expansion in high temporal resolution based on a marker tracking approach (Martrack Leaf) [2], available on the Plant Methods web site. This study used dark beads attached to the margins of a leaf and a camera fitted with a 940nm narrow bandpass filter. At this wavelength the leaf is brighter than the beads which makes image analysis easier.

[1] Pinto F, Mielewczik M, Liebisch F, Walter A, Greven H, et al. (2013) PLoS ONE 8(9): e73234. doi:10.1371/journal.pone.0073234
[2] Mielewczik M, Friedli M, Kirchgessner N, Walter A. Plant Methods 2013, 9:30 doi:10.1186/1746-4811-9-30

[Note: corrected information about the hyperspectral camera added 31 October]