A method for detecting the position of objects under a surface with respect to a reference Cartesian system S ( x , y ) having origin O and axes x and y , said method comprising the steps of: - prearranging a GPR apparatus , said GPR apparatus comprising: - a GPR sensor; - a distance detecting unit configured to measure a distance with respect to a not transparent object; - a control unit; - a centre of reference C ( x c , y c ) having coordinates x c and y c on said reference Cartesian system S ( x, y ); - prearranging a first linear wall , said first wall having direction parallel to said axis x of said reference Cartesian system S ( x,y ); - handling said GPR apparatus on said surface along a trajectory γ ; - detecting a first measurement of distance between said distance detecting unit and said first linear wall ; - processing said first measurement of distance by means of said control unit in order to calculate said coordinate y c of said centre of reference C ( x c , y c ); - repeating said steps of detecting and processing said first measurement of distance at time intervals τ in order to calculate a change of said coordinate y c during said step of handling; - associating a coordinate y i = y ci to an i-th object detected, where y ci is value of said coordinate y c at the detection by said GPR sensor of said i-th object ; said method characterized in that it also comprises the steps of: - verifying, on the basis of said change of said coordinate y c , that said trajectory γ coincides with a predetermined trajectory γ'; - in case that said step of verifying is negative, correcting said trajectory γ along which is carried out said step of handling. - prearranging a GPR apparatus , said GPR apparatus comprising: - a GPR sensor; - a distance detecting unit configured to measure a distance with respect to a not transparent object; - a control unit; - a centre of reference C ( x c , y c ) having coordinates x c and y c on said reference Cartesian system S ( x, y ); - a GPR sensor; - a distance detecting unit configured to measure a distance with respect to a not transparent object; - a control unit; - a centre of reference C ( x c , y c ) having coordinates x c and y c on said reference Cartesian system S ( x, y ); - prearranging a first linear wall , said first wall having direction parallel to said axis x of said reference Cartesian system S ( x,y ); - handling said GPR apparatus on said surface along a trajectory γ ; - detecting a first measurement of distance between said distance detecting unit and said first linear wall ; - processing said first measurement of distance by means of said control unit in order to calculate said coordinate y c of said centre of reference C ( x c , y c ); - repeating said steps of detecting and processing said first measurement of distance at time intervals τ in order to calculate a change of said coordinate y c during said step of handling; - associating a coordinate y i = y ci to an i-th object detected, where y ci is value of said coordinate y c at the detection by said GPR sensor of said i-th object ; - verifying, on the basis of said change of said coordinate y c , that said trajectory γ coincides with a predetermined trajectory γ'; - in case that said step of verifying is negative, correcting said trajectory γ along which is carried out said step of handling. <EOS>