The similarity between the general remote sensing integral equation and Dorman's integral equation relating secondary to primary muon variation spectra has been pointed out and exploited. Primary muon variation spectra and parameters of interplanetary field inhomogeneities are remotely sensed by a nonlinear inversion technique, using two different coupling functions. Results are compared to those obtained by the spectrographic technique and interpreted in terms of interplanetary field fluctuations. Based on relationships among kernels of the integral equation, optimization of location and orientation of measuring stations become possible.