A system comprises a computer that includes a processor and a memory. The memory stores instructions executable by the processor to estimate a first joint probability distribution of first data with respect to second data based on first and second marginal probability distributions of the first and second data, wherein the first data is from a first sensor based on a first sensor coordinate system, and the second data is from a second sensor based on a second sensor coordinate system, to estimate a second joint probability distribution of the first data with respect to the second data based on a projection of the first data onto a plane defined in the second sensor coordinate system, to estimate a rigid transformation between the first sensor coordinate system and the second sensor coordinate system by minimizing a distance between the first and second joint probability distributions, wherein the second joint probability distribution is a function of a set of extrinsic calibration parameters, and based on the set of the extrinsic calibration parameters, to detect an object in the first and second data.
