Sometimes, we need to compare datasets with different resolutions to establish a relation. I have to compare NDVI time-series with data having 250 meter resolution. Is it ok to create NDVI time-series in GEE using Landsat and then scale it to 250-meter or using MOD13Q1 250-meter (MODIS NDVI) will be better?
Most times, rescaling do affect the satellite image quality, and this often depends on the choice of software used, the method/process adopted for rescaling, and lastly the image file format (before and after the rescaling).
Yes, rescaling affects image quality.
As for landsat vs modis ndvi, instead of scaling landsat to 250m, modis seems better option as it will have better temporal resolution. Or you can try both. Since, you are using GEE with minor changes in the script you should be able to test both the imagery.
It is better to use same satellite images to analyze time series NDVI index.
You may have a look on this manuscript
Article Using shape extraction to enhance classification of Landsat ...
Good question. As Samuel Akande and Akshay Paygude already mentioned, there are several factors to consider. Although I do not know the application you have in mind, I think the most important factors here are the spatial and temporal alignment of the satellite data and the other data. In other words: Temporal: Do the Landsat or the MODIS data cover the same timespan in which the other data were covered? Were they recorded at the same time of day (NDVI may fluctuate during the day)? Spatial: Using MODIS because it has the same resolution may seem a good idea, but be aware that the pixels of MODIS and the cells of your other data may not fit, so you may need to resample, introducing errors, depending on the resampling strategy. In that case, it may be more precise to use the Landsat data and take the average NDVI of the Landsat pixels that fall within the cell of your other data for comparison.
Thank you and I appreciate the time you took to think about it and I find it to be very helpful. I will consider your suggestions. Wietske Bijker , Samuel Akande , Akshay Paygude , Hossam Abou-Shaara and Sher Bahadur Gurung.
It depends on your study target. If you put clouds in your consideration, MODIS 250 m is enough to construct the NDVI time series.
Yes, in most cases rescaling do affect the pixel resolution and quality. If it is from high to low resolution, it should be okay. If it's in a different way, you are actually spoiling the data.
rescalling effect the quality of image, but its depend on your purpose, why you are using satellite image.
yes definitely it varies with rescaling, for your study purpose we can improve the visualization using rescaling and we can prepare maps using GIS after image processing process
If you only consider spatial resolution as the major concern, upscaling from a high resolution to a lower resolution often gives a better accuracy than downscaling from a lower accuracy to a higher accuracy. Upscaling Landsat can give a better accuracy, when the effect from mixed response/fractional cover effects at 250 m resolution of MODIS is concerned. But, again it depends on the extent of your AOI and size of the land cover clusters.
Although it is possible to rescale the data, It is better to use the same satellite data. and that related to the differences in image resolutions.
regards
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