Presentation on the experiment, from a data analyst's perspective
Ashu Guru
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03/13/2019
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Presentation on the experiment, from a data analyst's perspective by Ashu Guru, Univ of Nebraska Raikes School. (4 mins)
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- [00:00:00.240]We have heard the scientist explain us the experiment.
- [00:00:03.720]Now we will take a look at the same experiment from the point of view of an analyst.
- [00:00:09.760]So we are interested in the canopy spectral reflectance that is CSR which evaluates the
- [00:00:15.680]amount of light reflected from the plant canopy.
- [00:00:19.660]The instrumentation that we are using is a spectroradiometer and the spectroradiometer
- [00:00:26.340]measures two bands of 2048 discrete wavelengths both upwelling and downwelling.
- [00:00:34.640]These are in the ranges 339.8 to 1024.1 nanometers and 591.3 and 1239.2 nanometers.
- [00:00:48.160]The experiment can be visualized as shown in these two side by side rectangles where
- [00:00:53.200]the left rectangle is showing
- [00:00:56.200]...
- [00:00:56.200]...
- [00:00:56.280]is showing 330 plots
- [00:00:56.320]330 plots with water stress treatment and the right is showing 330 lines of water non-stressed treatment.
- [00:01:02.820]There are 300 lines of wheat and there are two lines with 15 repeats so
- [00:01:10.460]that's where we get 330 sites. If the data is collected per day then we will have 330 upwelling
- [00:01:20.560]data files and then 330 downwelling data files and we will look at the relationship with the
- [00:01:26.300]yield as a response variable.
- [00:01:30.080]Some of the common spectral indices for measurements are listed here and one of the examples is
- [00:01:37.140]normalized difference vegetation and then this is the particular formula. This by no
- [00:01:43.220]means is the full list of all common spectral indices but just the ones that we are going
- [00:01:50.140]to refer to for the time being for this particular discussion. The scientist also mentioned
- [00:01:56.280]the objectives. The one that we will be looking at is which CSR indices and growth stages
- [00:02:02.840]best correlate with yield and/or yield components. So let's take a quick look at the data from
- [00:02:08.860]the sensor. So the screenshot that you are looking at is a file that shows the output
- [00:02:13.900]from the data sensor. The ones that I would like you to focus on right now is the column A,
- [00:02:19.570]where we see the different wavelengths that the instrument measures. And following column B
- [00:02:28.690]onwards, we see that these are the readings that were logged by the sensor or by the instrument
- [00:02:36.330]when the reading was taken in a particular plot for a particular treatment on a particular day.
- [00:02:44.190]So this is sample number 0, this is sample number 1, this is sample number 2,
- [00:02:48.930]this is sample number 3, and the wavelengths start from row number 11. You can see that there
- [00:02:57.170]are the first reading starts from 339.98 is at row number 11, and then the last reading is
- [00:03:04.830][scrolls through Excel sheet]
- [00:03:06.070]2058 which actually corresponds to my previous mention that the instrument measures 2048 discrete
- [00:03:21.670]wavelengths one thing I would also like you to notice is that for example let's see the index
- [00:03:27.010]red edge NDVI uses the wavelength at 750 so now if we look at this if we look at the data that we
- [00:03:36.550]have collected you may want to notice that there is 750 is not exactly a wavelength that is measured
- [00:03:51.110]by the instrument but it measured various wavelengths which are close to 750 so
- [00:03:56.990]this means that the scientists may actually be interested in averaging some wavelengths together
- [00:04:03.110]and considering the readings that were logged by that instrument for that set for a particular
- [00:04:10.310]wavelength referred in the index calculation. We will now proceed with working towards our main
- [00:04:19.130]objective which is that which CSR indices and growth stages best correlate with yield and or
- [00:04:24.950]yield components.
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