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Farm drones are hot!

Posted by Chris Anderson on June 23, 2013 at 8:30pm

3689532145?profile=originalThis magazine isn't online, but you can get it on your iPad, Kindle or Android tablet via NextIssue. The article is a pretty basic overview, with examples of using a Rite Wing Zephyr and a hexacopter along with a Canon s100 modified with the IR filter removed. But it's notable that drones are getting this kind of attention in agriculture. 

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  • Deon van der Merwe November 1, 2013 at 5:21am
    On the series of wavelength images: if you look closely at the detail, as opposed to the overall brightness, you will notice that where you have the densest chlorophyll (the trees), the brightness is actually best in the 720nm image. Some of the dark contrasting areas in the field at higher nm values, that appear bright in the lower nm range, are due to the strong NIR absorption by moisture at the higher NIR wavelengths. This effect may result in an apparent low plant biomass in those areas that is not related to the actual biomass. When interpreting an NDVI derived from the higher wavelengths for areas like the example where there are strong differences in soil moisture, there is a danger of misinterpretation as far as biomass is concerned.
  • Deon van der Merwe November 1, 2013 at 5:04am
    James, thanks for sharing the Event38 link. I was not aware of them.
    The graph they provide can be misleading. The graph shows % transmission, and not the sensor response. The MaxMax conversion has a very similar transmission graph, but the important parameter is the sensor response. I'm not sure why the colors in their example do not appear "correct", but it may just be related to how the image was processed.
    I'd like to see their camera compared to the MaxMax. If they are willing to let me do a head to head comparison, using the same methods and equipment on both, I'd be happy to share the results with the community here.
  • James Dunthorne October 31, 2013 at 8:09pm

    I hadn't realised you had done so much testing, i just wanted to ask some questions to ensure i am buying the right camera before i shell out a tonne of money! Thanks for the help though, i am relatively new to these cameras, i am used to operating UAVs so it may take me a little bit up time to get up to speed. Only a few weeks ago i was looking at tetracam and now i wouldn't touch it from what some people have said. This maxmax conversion is definitely the most promising camera i have seen so far, especially when combined with the Agpixel software. 

    Does anyone know how much Agpixel costs? I couldnt find a price anywhere :/

  • James Dunthorne October 31, 2013 at 5:30pm

    Anyone had a play with this? Looks like it might be a slightly better solution than the maxmax conversion...

    http://www.event38.com/ProductDetails.asp?ProductCode=CAM-NGB260

  • James Dunthorne October 31, 2013 at 5:22pm

    Comparing grayscales of a field at different wavelengths you might see what i mean (see below)

    Is the conversion going to be good for NDVI, because there isn't a massive amount of reflection in this scale. Not as much as there is at 800nm anyway.

    Cheers
    3692870845?profile=original

  • James Dunthorne October 31, 2013 at 4:45pm

    Thanks for the info guys.

    One problem i foresee with getting the maxmax conversion is that a true NDVI requires NIR light, and this starts at 760nm. The spectral intensity graphs shows that the conversion is not actually capturing any part of this spectrum. It is in fact a part of the spectrum inbetween red and NIR. Is this part of the spectrum actually good for looking at plant health?

    If a cheap camera existed which would measure R G B and NIR (760-1100nm), it would be perfect. The tetracam does 760-900nm in the NIR spectrum with R G NIR1 but is expensive and crap resolution. The maxmax conversion maxes out at 760nm, so im unsure how useful this will be for plant health detection.

    Does anyone know of any information regarding using these bands for crop health monitoring?

  • Deon van der Merwe October 31, 2013 at 1:35pm

    This image shows sensor characteristics from a MaxMax-converted S100. It was done using a diffraction grating and halogen light. The spectral calibration was done using a mercury lamp. It should be fairly accurate in terms of wavelength, but the peak magnitudes are not calibrated for the response in sunlight.

    3692871127?profile=original

  • Deon van der Merwe October 31, 2013 at 1:19pm

    I expect you will be happy with the results from a MaxMax camera. They use filters that preserve the ability of the camera to auto focus correctly, and you will not have hot spots or other artifacts.

    Many people use the SX260 with good results. I like the S100 (you have to call them to order one). It also has GPS, but it has a bigger sensor, exceptional dynamic range for a point-and-shoot, and it has  "DSLR-like" manual controls. Some people have experienced lens vibration wit the S100, but it only seems to be an issue on some aircraft. Probably due to the prop vibration frequency resonating with the floating lens.

  • James Dunthorne October 31, 2013 at 1:00pm

    I read through the maxmax website and i think i understand it now. Are there any spectral response graphs of these maxmax conversions? I am trying to look for stress in wheat maize rape and peas. Will this converted camera give me the data i need to detect a good NDVI picture? Also, any suggestions on cameras to use. I liked the look of the Canon SX260 as it can be hacked with CHDK and has GPS. Are there any other cameras which are better?

    Cheers for your replies btw, i appreciate the help

  • Deon van der Merwe October 31, 2013 at 12:48pm

    The NIR+G-2B/NIR+G+2B algorithm was actually created by Dan at MaxMax.com. 

    I created two related algorithms, one of them has a slight advantage over the MaxMax algorithm in most experiments: (NIR-G-B)/(NIR+G+B)

    The algorithm I designed outperforms the MaxMax algorithm because the blue and green bands are strongly correlated with each other, and combining their information usually results in a slightly better dynamic range compared to using the MaxMax algorithm or an NDVI based on a single visible band.

    With all that said, however, the difference in performance between the algorithms is usually not significant enough to be a real practical concern.

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