I've been looking around at different cameras that can be used for image analysis (NDVI, multi-spectral measurements and the like). It seems one of the important aspects of this kind of imagery is knowing the light you have at the time of image capture. I noticed that some higher end multi-spectral cameras(1) have a built-in light meter so the ambient reflectance is calculated for every image. I can find a lot of handheld light meters on the market, but are there any that log it's readings in a way that can be matched with the image capture time for post-processing of the images? I am guessing that this would solve a lot of the issues with comparing spectral information across datasets taken with converted point and shoot cameras or even with multi-spectral cameras where there reflectance targets on the ground aren't practical (i.e. large area of coverage).
I'm very new to this so please excuse any misconceptions you find. I also suspect that I just don't have the language to describe what I'm looking for and that's why I haven't found it yet...
Thanks
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Edit:
In looking further at these hand held light meters, they all have a 'light difuser' bubble over the lense. Let's say I had two converted Canon S100s, one pointed up and one down. The top one would have this bubble over the lens to difuse the light and it would take a picture at the same time as the downward facing camera. The resulting image from the top camera could then be used to normalize the light level of the downward facing camera through post-processing. Then it could be directly compared to images taken a month later.
One issue there might be with this is that the top camera would also need to be on a gimbal to ensure that it is always pointing straight up. Maybe set it so the cameras share one gimbal on the front of the copter. Any shadow or change in angle of the top camera would affect the amount of light it reads...