Matlab interpolation of a hemisphere to a finer grid

I've computed data on this hemisphere:

    % Compute hemisphere coordinates
    segments = 20;                                                              
    theta = deg2rad(linspace(-180,0,segments))';                                % Elevation (bottom half of a sphere)
    phi = deg2rad(linspace(-180,180,segments));                                 % Azimuth
    [phi,theta]=meshgrid(phi,theta);
    zObsG = obsRadius.*sin(theta);
    xObsG = obsRadius.*cos(theta).*cos(phi);
    yObsG = obsRadius.*cos(theta).*sin(phi);

I want to interpolate this data now to a finer grid with more elements:

    segmentsInterp = 100;                                                              
    thetaInterp = deg2rad(linspace(-180,0,segmentsInterp))';                                
    phiInterp = deg2rad(linspace(-180,180,segmentsInterp));                                
    [phiInterp,thetaInterp]=meshgrid(phiInterp,thetaInterp);
    zObsGInterp = obsRadius.*sin(thetaInterp);
    xObsGInterp = obsRadius.*cos(thetaInterp).*cos(phiInterp);
    yObsGInterp = obsRadius.*cos(thetaInterp).*sin(phiInterp);

I somehow struggle to use the interp or griddata functions in Matlab as it outputs for example: "The grid must be created from grid vectors which are strictly monotonically increasing." or "The number of input coordinate arrays does not equal the number of dimensions (NDIMS) of these arrays.". Any hints to interpolate the obtained data to the new grid?

Thanks a lot in advance!

[Koundinya]

how are you using the griddata and interp functions here ? It would be easier to understand the error if you post the complete code