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Contributor
Posts: 68
Registered: ‎03-13-2016

Any Possibility Using ERDAS IMAGINE to do conversion of Landsat 7 ETM DNs to Surface Reflectance

Dear Forum Members,

 

Greetings.  Please I need help and urgently too. I am in the middle of my research work and some pats has to do with remote sensing and image processing – an area which I ma not versed or highly skilled.

 

However, I have managed to scale some technical hurdles through online help and you tune tutorials.

 

I need help on

  1. How to convert digital numbers of image pixels to Surface Reflectance so that I can calculate NDVI. I am told that calculating NDVI with DNs especially when one is carrying out a time series analysis is not advisable
  2. I currently have ERDAS Imagine 2015 installed on my system.  Is there an inbuilt algorithm in ERDAS imagine that can be used in doing this?
  3. If not, what algorithm can I use ? and what options are available for this process?
  4. Please I would appreciate some clear step by step (bullet -pointed  ) directions on what to do
  5. Or if there are any online videos to show the steps , please point me to it

I thank you all in advance for this help. 

Highlighted
Technical Evangelist
Posts: 643
Registered: ‎02-02-2016

Re: Any Possibility Using ERDAS IMAGINE to do conversion of Landsat 7 ETM DNs to Surface Reflectance

ERDAS IMAGINE has a Landsat 7 Reflectance Conversion tool which will convert DN values to reflectance values. This tool is can be found on the Raster tab under the Radiometric menu.

 

The documentation thoroughly explains each of the input parameters - Landsat 7 Reflectance Conversion.

 

Regards,

 

Stephen Bent

Hexagon Geospatial Support

Highlighted
Contributor
Posts: 68
Registered: ‎03-13-2016

Re: Any Possibility Using ERDAS IMAGINE to do conversion of Landsat 7 ETM DNs to Surface Reflectance

Manythanks for your reply. At least it moved me from one level to another.

 

 

 However, i still have some concerns

 it is written on the Hexagon geospatial page that Only images imported into IMAGINE from Fast Format, 7A Acres, HDF, and NLAPS are supported. If you want to import something else, you will need to manually get all parameters from the image header files.

Please what does this mean? i am not familiar with these file formats.  I simply downloaded my images from earth explorer and they are all in GEOTIFF file formats. 

Does it then mean that I have to manually input the needed parameters for each band that I am converting ?

  1. While naming the output file name, I intend to leave them in .tiff formats since i will be computing NDVI after the SR conversion
  2. It is written in the hexagon geospatial:  Map Click to use map coordinates, if the data are rectified.

According to the Landsat documentation, all level 1 collection 1 data are rectified with correct GCPs and DEM.  I guess by proceeding with this step, i will be doing the right t thing

  1. Finally, I would be grateful if you can share with me any tuturial in video form develped by Hexagon on this Radiance to SR conversion so i can follow. 

 Thank you

 Emana

Highlighted
Regular Contributor
Posts: 279
Registered: ‎11-16-2015

Re: Any Possibility Using ERDAS IMAGINE to do conversion of Landsat 7 ETM DNs to Surface Reflectance

Hiya. Does this method convert to TOA or true surface reflectance? I can't see anything that takes the atmosphere into account and I've only ever used ATCOR for this. Cheers, Johnnie

Highlighted
Contributor
Posts: 68
Registered: ‎03-13-2016

Re: Any Possibility Using ERDAS IMAGINE to do conversion of Landsat 7 ETM DNs to Surface Reflectance

hello everyone,

 

I am here to glean knowledge from expert remote sensing scientists and those versed with the use of ERDAS inmage to preprocess images

 

My overall goal is to calculate NDVI in the 20 images that I have extracted so far

 

I have 20 images and I am using only 2 bands for my analysis although I stacked 3 bands initially

 

I am uisng Landsat ETM 7 images  (over 80% ) and Landsat 08 ( 15%) images

 

I retrieved them from Earth Explorer ( as a beginner , this is the only interface I am used to)

 

Now I am told that since I need to do a time series analysis that I need to convert the DNs ( since landsat collection 1 level 1 data are delivered in digital numbers or 8 bits) to surface reflectance values to account for atmospheric and solar illumination problems arising from differnet atmospheric conditions at different acquisition times.

 

I have read that converting from DN to Surface reflectance implies ABSOLUTE CORRECTION. And that absolute corection entails the following steps

  1. digital numbers to at-sensor radiance
  2. 2. at-sensor radiance to TOA ( this is solar correction)
  3. 3. TOA to SR  ( atmospheric correction)

Now my questions are

  1. What does ERDAS do? Does ERDAS convert directly from DNs to SR? thereby circumventing  these two steps:  DN to at-sensoor radiance and at-sensor radiance to TOA?

2.  However, having read through the tutorial offered by Hexagon Geospatial , I still have some concerns

 

 it is written on the Hexagon geospatial page that Only images imported into IMAGINE from Fast Format, 7A Acres, HDF, and NLAPS are supported. If you want to import something else, you will need to manually get all parameters from the image header files.

Please what does this mean? i am not familiar with these file formats.  I simply downloaded my images from earth explorer and they are all in GEOTIFF file formats. 

Does it then mean that I have to manually input the needed parameters for each band that I am converting ?

  1. While naming the output file name, I intend to leave them in .tiff formats since i will be computing NDVI after the SR conversion
  2. It is written in the hexagon geospatial:  Map Click to use map coordinates, if the data are rectified.

According to the Landsat documentation, all level 1 collection 1 data are rectified with correct GCPs and DEM.  I guess by proceeding with this step, i will be doing the right t thing

  1. Finally, I would be grateful if you can share with me any tutorial in video form developed by Hexagon on this Radiance to SR conversion so i can follow. 

 Thank you

 Emana

Highlighted
Contributor
Posts: 68
Registered: ‎03-13-2016

Re: Any Possibility Using ERDAS IMAGINE to do conversion of Landsat 7 ETM DNs to Surface Reflectance

Hello Stephen,

 

Thank you once more for your leading advice

 

I am getting familiarized with the software now .

 

However, here are a few quick questions

 

1.  Which is the most appropraite choice to select between these two?

Stretch to Unsigned 8 bit   

Ignore Zero in Stats.

 

2.  What output data type should I select at this point?  ( please dont forget that I still need to use teh SR values to compute NDVI)

 

3. My Landsat data are Collection 1 level 1 images which landsat says have been radiometrically and geometrically corrected. They are rendered in L1TP levels and are the highest quality.  In this case, which technique , should I use,

Bias/Gain    OR   LMAX/LMIN   ?

 

I thank you in advance for helping out.

 

Best regards

 

Kansy

Highlighted
Technical Evangelist
Posts: 153
Registered: ‎02-05-2016

Re: Any Possibility Using ERDAS IMAGINE to do conversion of Landsat 7 ETM DNs to Surface Reflectance

Have you looked into our Spatial Recipe- "Landsat 8 Top of Atmosphere Reflectance Conversion", which converts quantized DN to Top of Atmosphere Reflectance? 

 

http://community.hexagongeospatial.com/t5/Spatial-Recipes/Landsat-8-Top-of-Atmosphere-Reflectance-Co...

 

Regards

Partha Roy

Highlighted
Contributor
Posts: 68
Registered: ‎03-13-2016

Re: Any Possibility Using ERDAS IMAGINE to do conversion of Landsat 7 ETM DNs to Surface Reflectance


@ParthaR. wrote:

Have you looked into our Spatial Recipe- "Landsat 8 Top of Atmosphere Reflectance Conversion", which converts quantized DN to Top of Atmosphere Reflectance? 

 

http://community.hexagongeospatial.com/t5/Spatial-Recipes/Landsat-8-Top-of-Atmosphere-Reflectance-Co...

 

Regards

Partha Roy


Hello dear Roy,

 

many thanks for your reply and suggestion.

 

I will look that up and get back with updates.

 

Take good care

 

Emana

Highlighted
Contributor
Posts: 68
Registered: ‎03-13-2016

Re: Any Possibility Using ERDAS IMAGINE to do conversion of Landsat 7 ETM DNs to Surface Reflectance

Hello dear community members

 

I also have theh same questions are Johnie, does this model convert dorectly to Surface Reflectance or to TOA?

 

and if it does convert to TOA first , how can one proceed to converting from TOA to SR with ERDAS IMAGIBE?

 

Thank you everyone.

 

Emana