Change detection module

Microwave Toolbox
1

Hi, I used the change detection available in snap. I think it would be really useful to let the user the definition of the thresholds to be applied for the threshoding and not fix it to -2.0/2.0 (the thresholds are not always symmetric…). Moreover, I did not really understood what a mask is in snap: is it binary image? Is is possible to export it in a image format?

Thanks for your help!

1 Like
2

We’ll be updating change detection in the fall and include your suggestions.

3

Hi, it seems there is no documentation on the change detection in S1 TBX - any hints/urls about which methodology and how to apply this procedure?

Thanks,
Rasmus

4

Coregister two products and then run the change detection operator. It
just applies a log ratio. You can then use the colour manipulation to
threshold high positive values one colour and negative values another
colour. Everything in between you can make transparent by giving it no
colour. You can then overlay it over your master image using the Layer
Manager.

2 Likes
5

Is it necessary to apply orbit file for at first step (before coregisteration) in Change Detection?
if yes, what about new data that the precise orbits is not available?

Morteza

6

how can i make change detection on two ndvi raster with expression in raster calculator

7

both NDVIs need to be in the same product, so creating a stack is the first step (unless both rasters have the exact same dimensions and pixel numbers).

Then you can access both in the band maths and formulate an expression

NDVI2 - NDVI1

8

thanks yes i do the same NDVI2 - NDVI1 the result is raster change detection but i want to reclassify in multiple classe

9

you can define a threshold which indicates where change occured by combining two steps:

  1. difference: NDVI2-NDVI1
  2. change: difference > 0.2

or if you want changes in both positive and negative directions:

  1. difference: abs(NDVI2-NDVI1)
  2. change: difference > 0.2
10

THANKS ABRAUN
I DID NOT understand what do you mean by abs and i want to know why you are shoosing 0.2
IN FACT I WANT TO whrite an expression in raster calculator that give me three classes
first for change positive
secende for change nagative
third for no change
im looking fo How to whrite a correct expression

11

This can be achieved with the IF, THEN and ELSE commands in the band maths. Open the extended dialogue and use the items from the drop down menu

12

thanks for helping me

13

hello Abraun i want to downlaod citation about sen2COR IN ORDRE To itegrate it in may paper
can helping me

14

How about one of those:

  • Main-Knorn, M., Pflug, B., Louis, J., Debaecker, V., Müller-Wilm, U., & Gascon, F. (2017,): Sen2Cor for Sentinel-2. Image and Signal Processing for Remote Sensing XXIII 10427, p. 1042704. doi: 10.1117/12.2278218
    https://core.ac.uk/download/pdf/145232625.pdf

  • Louis, J., Louis, Debaecker, V., Pflug, B., Main-Korn, M., Bieniarz, J., Mueller-Wilm, U., Cadau, E., & Gascon, F. (2016): Sentinel-2 Sen2Cor: L2A Processor for Users. Living Planet Symposium 740, p. 91.
    https://core.ac.uk/download/pdf/77231474.pdf

Maybe @bdpg can comment if this is correct.

15

thanks Abraun is it possible to download directly citation to integrate it in endnote

16

use google scholar and click on this icon grafik below the desired publication.

https://scholar.google.com/scholar?q=sen2cor

17

Helo forum I want your help on the way to produce soil moisture content map.I have read some articles saying that we can produce soil moisture map from two consecutive image using change detection method and i want to know what are the steps to produce the map from two consecutive image

18

please have a look at johngan’s explanations in this topic: Soil moisture identification -Sentinel and also in this post: Soil moisture mapping using Sentinel-1-Data and SNAP?