Can't Add bathymetry and elevation bands and masks

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antu
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Can't Add bathymetry and elevation bands and masks

by antu » Tue Aug 01, 2017 1:06 am America/New_York

Hello experts,I want to find the chlorophyll data at several depth. For that reason, I am trying to "add bathymetry and elevation bands and masks" in windows. I tried it both 9 km and 4 km product and also use "coastline and land mask " and " bathymetry and elevation bands and mask" in combination. But nothing can't get me the data of specific depth. How can I do this in windows ?Thanks all.Have a good day !

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gnwiii
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Answers: 1

Can't Add bathymetry and elevation bands and masks

by gnwiii » Tue Aug 01, 2017 8:26 am America/New_York

You need to provide more details.   What data are you using?   Are you able to create a bathymetry mask for your desired range of depths?  How do you plan to use the mask (e.g., do you want statistics for the chlor_a in the given range of depths)?

A common "use case" is to obtain statistics for chlor_a in various depth ranges, e.g., 0--200m, 200--1000m, etc.   By "specific depth" do you mean you just want pixels for depths close to some given value?  Bathymetry data are often provided as integer data in meters, but for areas with a steep slope the depth may skip several meters over the size of one satellite pixel, so in practice you may need to use a depth range of several meters. For example, if your specific depth is 40.5m, a bathymetry mask for 40-41 m. will have many gaps, while a range of say 38 to 42 m will have fewer gaps, but also wide areas where the bottom has a shallow slope.

An alternative approach is to create vector data for a specific depth contour.  In seadas you can use "Layer/Contour" to create contour lines for specific depths.  In file manager this should give you a new vector in File Manager.   You can save this as a shapefile, then convert the shapefile to a CSV file that can be used as a "point data source" in a "correlative plot" or with pixel extraction to generate an ASCII file with chlor_a values along the contour line.  See the "Ship Track"
and "Pixel Extraction" slides in  Ocean Optics XXII SeaDAS Workshop

antu
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Joined: Mon Mar 02, 2020 11:08 pm America/New_York

Can't Add bathymetry and elevation bands and masks

by antu » Wed Aug 02, 2017 6:42 am America/New_York

Hello gnwiii,
Thanks for your reply. I basically want to calculate chl-a concentration from 0 to 250m depth. So, i want to create  a bathymetry band and mask thats why I can statistical analysis of chl-a concentration (0-250m) depth water.

In contour, It gives line for a range of chl-a value.

If it is not possible, I will use polypine and draw a geometry and make a vector file. But this process is not precise. Using batheymetry will help me more.

Thank.

OB.DAAC - SeanBailey
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Can't Add bathymetry and elevation bands and masks

by OB.DAAC - SeanBailey » Wed Aug 02, 2017 8:03 am America/New_York

If you are looking for a way to obtain chlorophyll concentration at various depths within the water column, that is not possible with satellite remote sensing.  If you are looking to define an area based on the 250m isobath for limiting the data for your study, that is exactly why we include the bathymetry tool in SeaDAS :smile:

We have several tutorials on the use of SeaDAS.  There is a video tutorial on the use of the bathymetry tool that may be of help to you.

Sean

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Can't Add bathymetry and elevation bands and masks

by OB SeaDAS - knowles » Wed Aug 02, 2017 8:50 am America/New_York

Your statement "In contour, It gives line for a range of chl-a value" is incorrect, unless I don't correctly understand your meaning.  A contour line is set to a specific value and not a range of values.  The GUI does have a range component, but this is a merely a user convenience feature for creating multiple contour levels. 

A note: the currently posted YouTube video is of an earlier SeaDAS version.  It is a useful video.  Just be aware that the current version of SeaDAS calculates true bathymetry (accounting for elevated lakes) whereas the earlier version in the video only computed elevation.

Right now the bathymetry tool only works in the GUI and not at the command line (GPT).  This tool is located under Layer > Bathymetry & Elevation.  This tool generates a band called "bathymetry" and a mask called "BATHYMETRY_MASK".  You set the depth range of the mask in the GUI or subsequently you can edit the range within the Mask Manager.  For more on this there is also a SeaDAS masking video: masking video.

Danny

gnwiii
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Answers: 1

Can't Add bathymetry and elevation bands and masks

by gnwiii » Wed Aug 02, 2017 9:41 am America/New_York

The SeaDAS 7 GUI is very complex, so takes some time to learn.   Assuming that you are interested in statistics for surface (satellite) chlor_a, you aren't trying to do anything unusual, so you are probably missing a small step that experienced users do without even thinking. 

The tutorial linked in Sean's post should help with the bathymetry band and mask.   You may also want to look at the masks tutorial and the sea surface temperature case study.  If the statistical analysis goes beyond what can be done using Analysis/Statistics, you can also export the chlor_a and bathymetry bands to geotiff or netcdf, etc. or extract ASCII data with chlor_a concentration and bathymetry for use with other software (stats or GIS packages).

antu
Posts: 30
Joined: Mon Mar 02, 2020 11:08 pm America/New_York

Can't Add bathymetry and elevation bands and masks

by antu » Sat Aug 05, 2017 12:38 pm America/New_York

Thanks SeanBailey, knowles and gnwiii. You peoples are awasome.

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