A method for detecting the position of objects under a surface with respect to a reference Cartesian system S ( x, y) having origin O (0,0) 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.