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Author Topic: Effects of mosaicing on vegetation index values  (Read 2286 times)

Andreas_BN

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Effects of mosaicing on vegetation index values
« on: January 06, 2016, 01:03:44 AM »
Dear all,

the recent scientific publication Rasmussen et al. (2016): Are vegetation indices derived from consumer-grade cameras mounted on UAVs sufficiently reliable for assessing experimental plots? In: European Journal of Agronomy 74, 75-92 assesses whether vegetation indices derived from UAV-mounted consumer grade cameras are affected by the stitching process, among other questions. The study looks at the software packages Microsoft ICE and Pix4D and finds that VI values are affected during the stitching process especially when using images taken in sunny conditions (i.e. exhibiting strong angular variation in reflectance).
My questions are:
  • Is there anybody in this community who has investigated the effects of mosaicing UAV-imagery on VIs using Agisoft?
  • What do you do to minimise the effects?
Thanks!
Andreas

photogrammetrix

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Re: Effects of mosaicing on vegetation index values
« Reply #1 on: January 06, 2016, 02:14:26 PM »
Hi Andreas,

I would be interested to take a closer look into this paper. Is there a link where I can download this?

From my point of view, deriving reliable values for  vegetation indizes from NIR-converted consumer-grade cameras is not at all an easy task, as often is suggested.

The concept of vegetation indizes was originally developed using multispectral sensors (for example Landsat Multispectralscanner MSS or Landsat Thematic Mapper TM) with well defined imaging parameters and spectral characteristics.  Furthermore there is additional information recorded during imaging which enables us to do a radiometric calibration - and if necessary, to correct also for atmospheric effects. Otherwise the image data and derived data such as VI will hardly be comparable between different acquisition dates and between different sensors.

The question I have in mind is, how much effort is necessary to get radiometrically calibrated measurements for the wavelength of interest from consumer-grade camaras, in order to derive comparable values for vegetation indizes - comparable over time and comparable between different sensors / consumer-grade cameras?


kind regards