Re: area calculation

[Mick.Spillane@xxxxxxxx]

On Thu, 12 Feb 2004, Wendy Wang wrote:

> Can Ferret calculate a surface area given Lat. and Lon.?
> Will the land area be taken into account?

Hi Wendy,
	I think using one of the topographic datasets you
could get a good representation of sea/land areas.

For example, try calculating the area of Australia and the
area of the sea in the region/x=100e:160e/y=45s:10s

use etopo5
let land=if(rose gt 0)then 1 else 0
let sea =if(rose le 0)then 1 else 0
shade/lev=(1)/nokey/pal=black land

list land[x=@din,y=@din]
!             VARIABLE : IF(ROSE GT 0)THEN 1 ELSE 0
!             FILENAME : etopo5.cdf
!             FILEPATH : /home/shiva/data/
!             LONGITUDE: 100E to 160E (XY integ.)
!             LATITUDE : 45S to 10S (XY integ.)
!          7.556E+12 square meters.
!!!! or 7.648E+12 m^2 if etopo2 is used !!!!
!
! These agrees quite well with the atlas-listed value of
! 7682300 sq km for the area of Australia.

list sea[x=@din,y=@din]
!             VARIABLE : IF(ROSE LE 0)THEN 1 ELSE 0
!             FILENAME : etopo5.cdf
!             FILEPATH : /home/shiva/data/
!             LONGITUDE: 100E to 160E (XY integ.)
!             LATITUDE : 45S to 10S (XY integ.)
!          1.512E+13 square meters
! the combined area (2.267E+13 m^2) agrees will with
! (160-100)/360 times the zonal area for a perfect sphere.
!            2*pi*(R^2)*{sin(45) - sin(10)}
let d2r=atan(1.)/45 ; let r=6371 ; let pi=4*atan(1.)
list ((160-100)/360)*2*pi*r^2*(sin(d2r*45)-sin(d2r*10))
! which gives 2.267E+07 sq.km

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