# convert the north azimuthal equal area EASE-grid (NL) map to regular lat/lon

From: Xianwei Wang <xianweiw_at_nyahnyahspammersnyahnyah>
Date: Thu, 11 Sep 2008 10:53:15 -0700 (PDT)

Hi,
I want to convert the north azimuthal equal area EASE-grid (NL) map to
regular lat/lon,
E.g., AMSR-E snow water equivalent (SWE) is at North Azimuthal equal area
EASE-grid (L). I want to convert /rebinning it into climatic grid or
regular lat/lon grid. What I did is:

(1). Calculate the latitude and longitude, lat_2d (rows, cols) and lon_2d
(rows, cols)/(721,721) , at each grid using the NL equations in the
document: EASE-Grid: A Versatile Set of Equal-Area Projections and Grids
at http://nsidc.org/data/ease/ease_grid.html
In calculation, I only output the lat/lon when x^2+y^2 =<r0^2+s0^2
(r0=360, s0=360, x=i-r0, y=j-s0, i and j are cols and rows from 0-720) to
make sure each pair lies inside the circle of the North Hemisphere. Grids
offset the circle is set as missing. Meanwhile, I also simulate a cell
value, cv=abs(sin(y/(x^2+y^2)), to test the rebinning.

(2). Use the ncl function rcm2rgrid (see
http://www.ncl.ucar.edu/Document/Functions/Contributed/rcm2rgrid_Wrap.shtml
) to re-binning/re-sampling/re-griding the NL ease grid into cylindrical
ML lat/lon grid (293x1383).
cv_rcm=rcm2rgrid(lat_2d, lon_2d, cv, lat_1d, lon_1d,1)

Now. My problem is:
the final output cv_rcm only have value at about 30 lines of lower
latitude (<10 degreeN), missing values for all other grids

(3). I also try functions of natgrids() and dsgrid2(), but these two
functions required no missing values. Obviously, the AMSR-E SWE data have
many missing values that can not be filled.

My question is what function should I use to rebinning the NL EASE-grid to
regular lat/lon grid?

Thanks.

Xianwei Wang

Department of Earth System Science
University of California-Irvine
Irvine, CA 92697
Tel: 949-824-1571

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Received on Thu Sep 11 2008 - 11:53:15 MDT

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