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Contributor
Posts: 68
Registered: ‎03-13-2016

Re: Basic Layer Stack Question

Dear Ian,

 

Many warm thanks for reply.

 

now I am through with Landsat destripping  process using ERDAS IMAGINE 2016.

 

I now want to proceed to converting DN values to SR

 

BUt the link  which I was referred to by one of your staff, Bent  ( https://hexagongeospatial.fluidtopics.net/reader/DEL_JLLyZd~_Z_8n4dW2rg/bLpf_6ChibeKMsnCLbC5hg) simply says conversion to reflectance but doesnt specify if it is SR or TOA

 

does it imply that a conversion from DN to TOA has to be carried out first before proceeding to a  TOA - SR  conversion.

 

How can one get around a TOA to SR conversion with ERDAS IMAGIBE?

 

Thank you Ian

 

 

Technical Evangelist
Posts: 732
Registered: ‎10-01-2015

Re: Basic Layer Stack Question

Hi Emana,

 

One of the simplest things is to simply make sure you order your data from USGS in the format that has already been corrected to surface reflectance. See

 

https://landsat.usgs.gov/landsat-surface-reflectance-high-level-data-products

 

But not all dates are available as SR products. So the next alternative for correcting to surface reflectance (i.e. applying atmospheric correction) is the great set of tools available through GEOSYSTEMS in Germany - the ATCOR Workflow for ERDAS IMAGINE

 

https://www.geosystems.de/en/products/atcor/atcor-workflow-for-imagine/overview/

 

In the next release of ERDAS IMAGINE (2018) we'll have a generic equivalent of the Rapid Atmospheric Correction operator called (not unsurprisingly) Generic Atmospheric. This will enable you to correct many different types of satellite imagery to surface reflectance so long as you can mine the necessary metadata information from the header files. It certainly should be possible with Landsat 7.

 

Cheers

 

 

 

Ian Anderson
Chief Product Owner, Desktop Remote Sensing
Hexagon Geospatial
Contributor
Posts: 68
Registered: ‎03-13-2016

Re: Basic Layer Stack Question

Hello Ian

 

Many thanks for your support.  Please see under each line of yours my response.

 

One of the simplest things is to simply make sure you order your data from USGS in the format that has already been corrected to surface reflectance. See

 

(I already did that few months ago but the products are not here.  Secondly, due to my temporal window of interest over my AOI and my research theme, I am unable to avoid using the SLC off datasests which are the only available datasets which needs to be cleaned up.  I wrote to Landsat and landsat says that although they have SR over my AOI, they have not carried out any destripping or gap-filling process. Hence , I resorted to manually cleaning up the images and then carrying out atmospheric correction. All my datasets are landsat 7 ETM+.

 

I can see that ERDAS has Landsat 7 conversion tool. but the fundamental question is does it convert only for TOA? or also for SR?

 

https://landsat.usgs.gov/landsat-surface-reflectance-high-level-data-products

 

But not all dates are available as SR products. So the next alternative for correcting to surface reflectance (i.e. applying atmospheric correction) is the great set of tools available through GEOSYSTEMS in Germany - the ATCOR Workflow for ERDAS IMAGINE

 

( Please could you clarify a little about the ATCOR? Do I need to a license from ATCOR to run this? or i can carry this out with my ERDAS IMAGINE 2016 access from the university.  Please could you supply a little more details?

 

https://www.geosystems.de/en/products/atcor/atcor-workflow-for-imagine/overview/

 

In the next release of ERDAS IMAGINE (2018) we'll have a generic equivalent of the Rapid Atmospheric Correction operator called (not unsurprisingly) Generic Atmospheric. This will enable you to correct many different types of satellite imagery to surface reflectance so long as you can mine the necessary metadata information from the header files. It certainly should be possible with Landsat 7.

 

Finally, I have been trying to do a simple subset of my landsat images using my AOI polygon as descried in this video from ERDAS.

 

http://community.hexagongeospatial.com/t5/ERDAS-IMAGINE/Subsetting-an-Image-with-a-Shapefile/ta-p/48...

 

I have been on this simple procedure for two days now . I have followed the video religiously but the problem i am having is that I am unable to select the AOI polygon from the viewer as done in the video ( that is i cant see teh faint dotted borders aroudn the AOI polygon ) so that I can see it and make changes to the style.

 

I then carried out the sub-setting in Arc GIS using teh Extract by mask tool  and tried to open the sub-setted landsat band which i sub-setted in arc map GIS in ERDAS  (since i am going to be carrying out my further analysis in ERDAS ) but I can not open the sub-setted  Raster image

 

Any clue Ian?

 

Many thanks

Regular Contributor
Posts: 215
Registered: ‎11-16-2015

Re: Basic Layer Stack Question

Hiya. Regarding the subsetting using AOI - there's no need to change the style. I've been using AOIs for years and years and have never felt the need to change the style. You can easily select an AOI by clicking inside the AOI polygon and you can confirm it's selected by noting the blue grab handles around the polygon, as in your attached image. Once it's selected like this you can use it as per the subsetting video. Cheers, Johnnie.

Contributor
Posts: 68
Registered: ‎03-13-2016

Re: Basic Layer Stack Question

Hey Johnnie thanks

 

let me clarify this.

 

Just as shown in thsi video  (http://community.hexagongeospatial.com/t5/ERDAS-IMAGINE/Subsetting-an-Image-with-a-Shapefile/ta-p/48...)

 

 

I want to select the AOI polygon over the ratser image by clicking the AOI in the viewer to select it so that I am able to maybe tweak around with the border lines nad make it more visible for me. Then later save teh created AOI polygon somewhere so I can use it for a later use.

 

But unfortunately after removing the shappe file from teh TOC, and clicking the area where the AOI polygon was displayed , I am unable to select the AOI in teh viewer just as it is shown in the short video turorial. I do not know why?

 

Emana

Regular Contributor
Posts: 215
Registered: ‎11-16-2015

Re: Basic Layer Stack Question

Are you sure that a) you created the shapefile successfully and b) you didn't delete the AOI when you deleted the shapefile? Try just turning off the shapefile layer in the Contents Pane. You can save the AOI by RH clicking on the AOI layer in the Contents Pane and selecting Save Layer as...

 

 

Contributor
Posts: 68
Registered: ‎03-13-2016

Re: Basic Layer Stack Question

Dear Ian,

 

PLEASE I NEED SUPPORT AND URGENTLY TOOgiven input.PNGGap-filled SR versus Ungapfilled SR.PNGGappedFilled Level 1 vs Raw SLC-level 1.PNG

 

I am not using the spatail modeler created by Geo sterlings in teh UK but I am using the import manager tab in ERDAS Imagine to do a direct import but getting an error message as shown in teh attached screen shot

 

I am using ERDAS 16.1

 

I am also usiing the reprocessed  LAndsat collection 1 tier 1  images whose naming and momenclature have been changed and i guess that is why the import manager is unabel to import the data directly.

 

I am weary of using the spatial modeller because i intend to do a slc-off gap filling using each band from different images so i do not want a stacked image.

 

secondly, i read here on Hexagon geospatial web page that in successfully carrying out  aTOA conversion, the Landsat 7 TOA conversion will only work with data imported 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. (and I am thinking that by directly using the import manager, I will circumvent all the manual inputing of header information)

 

I tried changing the way the datasets are named in currecnt collection 1 tier 1 nomenclature to the old way just as you suggested earlier but when i went back to the import manger, to the input field , the dataset i had changed the naming to the old nomenclature was not visible!!!!!!

 

As you can see the second set of image is the surface reflectance products. the one to the left is the one i have gap filled using the method from USGS web page and the image to the right is a surface rekfectance that has not been gapped filled

 

The last twin image is the level 1 Tier 1 collection  image. the one to the left is the one that has been gap filled and teh one to the right is the one that has not been gapped filled. all o fteh them have same (standard deviation stretch ) radiometry adajustment.

 

Pleae help with your inputs.

 

All i need at the end of the day is to derive NDVI values. but i understand that i need SR datasets not those with raw DN values

 

Kansy

 

Staff
Posts: 581
Registered: ‎02-02-2016

Re: Basic Layer Stack Question

Hi Kansy,

 

If you need urgent support you should submit a support ticket through our Support Portal (if you are in North America) or contact your local Hexagon Geospatial partner who provided your ERDAS IMAGINE license and they will provide assistance. The Support ERDAS IMAGINE forum is meant to foster discussion amongst the user community.

 

The USGS altered the naming format of their *.tar.gz zipped compressed files, using the product ID instead of the scene ID for the filename. This causes a problem with the Landat-8 from USGS importer which expects the filename to use the scene ID. The solution is to change the name of the *.tar.gz file to match the scene ID. Open the scene’s metadata file (*product-id*_MTL.txt) and look for the LANDSAT_SCENE_ID number and use this as the filename. For example, the downloaded file “LE07_L1TP_044033_20030531_20160928_01_T1.tar.gz” should be renamed to ‘LE70440332003151EDC00.tar.gz”. Make sure that you keep the *.tar.gz filename extension. This Landsat 7 or Landsat 8 from USGS importer does not import the reflectance values. It only imports the raster data.

 

Regards,

 

Stephen Bent

Hexagon Geospatial Support

 

Contributor
Posts: 68
Registered: ‎03-13-2016

Re: Basic Layer Stack Question

Hurray ! Hurray

 

Dear Stephan Bent, I made it!!!!!!!

 

Your reply was very clear and helpful.

 

I struggled through these trials

 

First I copied teh scene ID as you instructed from teh meta data and used it to change the namimg but I added ( .tar.gz) at teh end and when i tried to import through teh import manager, I saw that the folder was named as LE71880542000016SGS00.tar.gz .gz and it didnt work

 

So i tried again , this time adding only the .tar to the end of the name without ( .gz) at the end of the scence ID Number and behold, I scaled through.

 

I am energized to solve the next problems now.

 

which is converting DN to reflectance hoping that with the successful import of this data, the header information and all gap masks files that i will need in teh conversion process will be already available .

 

But here I have a critical question, does the Landsat 7 Reflectance Conversion really convert to Surface reflectance or to TOA?

 

I need to calculate NDVi and I am told I need to use SR units not DNs since my datasets are up to 17 units ( one per year)

 

I am so thankful for the remote support from Hexagon Geospatial community . It has really been very helpful and I will acknowledge this in my final thesis.

 

Many many warm thanks Stephan

 

Kansy

Contributor
Posts: 68
Registered: ‎03-13-2016

Re: Basic Layer Stack Question

Dear Bent, Anderson and Johnnie,

 

Good day All.

 

I successfully renamed all the new Tier 1 Level 1 landsat scenes using teh Scene ID in the Meta File. With this action, I successfully imported my data from 1999 till 2012.

 

But ERDAS is telling me that with 2013 till 2017 data ( even with applying similar copying and pasting to replace the scene name), that the images are not in the USGS format.

 

I have double checked the scene ID and everything seems ok.

 

However, I have observed that with 1999 - 2012 data the ending is LE71880542012337ASN00.tar

whereas from 2013 - 2017 , ending is SG100 as you can see highlighted LE71880542014006SG100.tar

 

Please any suggestion dear Colleagues?

 

Now I am stuck again!!!!

 

Kansy

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