Re: [ferret_users] vertical weighted averagng

["Ansley C. Manke" <ansley.b.manke@xxxxxxxx>]

Hi all,

Here are some related resources:

The @AVE transformation. Note that the @WGT transformation returns the weights used by the equivalent @AVE transform.

A section on General Information on transformations.

FAQ on averages computed on the surface of the earth

Here's a Users List archive message about calculating the area of grid cells on the Earth's surface - which is a technique that works in general - it's equivalent to @WGT in fact.
http://www.pmel.noaa.gov/maillists/tmap/ferret_users/fu_2004/msg00026.html


Ansley

On 3/23/2017 10:12 PM, Abhishek Savita wrote:

Hi... all

         I have also faced same problem earlier. I have checked  it analytically as well as with the matlab also. Actully ferret gives the weighted average if we give like var[x=@ave,y=@ave,z=@ave,.....]. But If anybody interested to compute normal average then in place of giving X, Y etc we should give corresponding index number as var[i=@ave,j=@ave,.....]. Where i and j are the index number corresponding Lon and lat.

Please check it I hope it will work.

with regards
Abhishek

On Fri, Mar 24, 2017 at 9:55 AM, Ryo Furue <furue@xxxxxxxxxx> wrote:

Hi Robert and Martin,

yes? list/k=1 temp[x=@ave,y=@ave]

...

      -1.788

but I'd like to have area weighed averaged value. How should I told ferret that x and y is long and lat for averaging computations,

With temp[x=@ave,y=@ave], Ferret does compute the area weighted average if the horizontal axes are longitude and latitude.  If the axes aren't longitude and latitude, Ferret computes x=@ave and y=@ave separately (I think), which may not coincide with the correct area-weighted average.

I don't know if it's possible to compute the area of each gridbox within Ferret. You may have to supply that information from outside. Then,

  let area_temp = temp * boxarea

  let area_average_temp = area_temp[x=@sum,y=@sum] / boxarea[x=@sum,y=@sum]

Ryo

--

Regards
Abhishek Savita

Research Scholar (Earth System Science Technology)

Center For Oceans, Rivers, Atmosphere & Land Science Technology
Indian Institute of Technology, Kharagpur
+91-8609704619