How to extract satellite measured chlorophyll-a (chl-a) in MATLAB

Hi Folks,

I was using thie following script to extract chlor_a variable with lat[0S 30N] and lon[30W 100E] further need to capture the data values of chla for particular region esp for North Indian Ocean lat, long range

 ncdisp = ('A20150012015008.L3m_8D_CHL_chlor_a_4km.nc');
 lat = ncread('A20150012015008.L3m_8D_CHL_chlor_a_4km.nc','lat');
 lon = ncread('A20150012015008.L3m_8D_CHL_chlor_a_4km.nc','lon');
 chlor_a = ncread('A20150012015008.L3m_8D_CHL_chlor_a_4km.nc','chlor_a');
 % Load longitude array:
 lon = double(ncread('A20150012015008.L3m_8D_CHL_chlor_a_4km.nc','lon'));
 ind1 = find(lon>=30 & lon<=100);
 % Do the same for lat:
 lat = double(ncread('A20150012015008.L3m_8D_CHL_chlor_a_4km.nc','lat'));
 ind2 = find(lat>=0 & lat<=30);
 % Clip lat and lon to their specified range:
 lat = lat(ind2);
 lon = lon(ind1);
% Make a grid:
[Lat,Lon] = meshgrid(lat,lon);

Looking forward to your valuable suggestions

regards

Answer 1

[KSSV]

Let lon,lat be your grid coordinates of the nc file.

[X,Y] = meshgrid(lon,lat) ; 
xi = linspace(30,100) ; 
yi = linspace(0,30) ; 
[Xi,Yi] = meshgrid(xi,yi) ;
iwant = interp2(X,Y,chlor_a',Xi,Yi) ; 

If the data is 3D run a loop.

[Karthik M]

Hi @KSSV

Thanks for the response

I am still not finding to extract and retrieve data for the particular region coordinates of the grid : 0 S, 30 N, 30W,100E .

I need to extract point data for the required grid spatila extent, please see the attached netcdf file

https://oceandata.sci.gsfc.nasa.gov/MODIS-Aqua/Mapped/8-Day/4km/chlor_a/2016/

thanks and regards

[KSSV]

It is asking me to login to check the file.

[Karthik M]

usr id : karthi783

pwd: kARTHIK07

[KSSV]

What if I hack all your accounts? ;)

[Karthik M]

I want the output and result from the data the file size was large, shared my account details

[KSSV]

ncfile = 'A20160012016008.L3m_8D_CHL_chlor_a_4km.nc' ;

lat = ncread(ncfile,'lat');
lon = ncread(ncfile,'lon');
chlor_a = ncread(ncfile,'chlor_a');

[X,Y] = meshgrid(lon,lat) ;

xi = linspace(30,100,1000) ;
yi = linspace(0,30,1000) ;
[Xi,Yi] = meshgrid(xi,yi) ;
iwant = interp2(X,Y,chlor_a',Xi,Yi)' ;
pcolor(Xi,Yi,iwant') ; shading interp ;
colorbar

[Karthik M]

Thanks @KSSV will ping for any further queries

[KSSV]

Thanks is accepting/ voting the answer. :)

[Karthik M]

Hi @KSSV

I want to save my outputs as a different nc file having same lat, lon and chlor_a as it had before not in .mat file extension

I used this following example script but finding error

lon=(65:0.5:95)';
lat=(3:0.5:35)';
data=randi(20,65,61,365);
nccreatewrite('test1.nc','lat',{'lat','c'},lat)
nccreatewrite('test1.nc','lon',{'lon','c'},lon)
nccreatewrite('test1.nc','TC',{'lat','lon','days'},data)

kindly help

regards

[KSSV]

First you need to create the variables, read about nccreate.

[Karthik M]

Hi @KSSV

I tried using this script still error persist

nccreate('myfile.nc','myvar')

>> A = 99;

>> ncwrite('myfile.nc','myvar',A)

>> S = ncinfo('myfile.nc');

>> file_fmt = S.Format

file_fmt =

'netcdf4_classic'

>> S.Format = 'netcdf4';

>> ncwriteschema('newfile.nc',S)

kindly help

[Karthik M]

Hi @KSSV

I tried using this script still error persist

nccreate('myfile.nc','myvar')

>> A = 99;

>> ncwrite('myfile.nc','myvar',A)

>> S = ncinfo('myfile.nc');

>> file_fmt = S.Format

file_fmt =

'netcdf4_classic'

>> S.Format = 'netcdf4';

>> ncwriteschema('newfile.nc',S)

kindly help