function [sp2,ustar]=spshfttc(sp1,z1,z2,Ta)
% SPSHFTTC: adjusts wind speed from z1 to z2 following Smith (1988).
% sp2 = SPSHFTTC(sp1,z1,z2,Ta) shifts the wind speed sp1 measured at z1 to
% z2 using the neutral drag coefficient given the wind speed and air
% temperature at height z following Smith (1988), J. Geophys. Res., 93,
% 311-326. Assumes z1 and z2 scalars. Ta may be a constant. 
%
%   INPUT:  sp1 - measured wind speed [m/s]
%           z1 - measurement height [m]
%           z2 - desired height [m]
%           Ta - air temperature ([C] (optional)
%
%   OUTPUT: sp2 - predicted wind speed [m/s]
%           ustar - fiction velocity  [m/s]

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% 3/8/97: version 1.0
% 8/27/98: version 1.1 (revised to use CDNTC efficiently by RP)
% 8/5/99: version 2.0
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% set constants
as_consts;

if nargin==3,
  Ta=Ta_default;
end;

% find cd and ustar
[cd,sp10]=cdntc(sp1,z1,Ta);

ustar=sqrt(cd).*sp10;

sp2=sp10+ustar.*log(z2./10)/kappa;