A system for detecting the road condition ahead of a vehicle, the system comprising: at least one detector with first and second spectral filters configured to measure radiance of the road in spectral bands adjacent to a crossover point of the imaginary parts of the indices of refraction of liquid water and ice, the at least one detector configured to measure the radiance in a first band having wavelengths in a spectral band on a first side of the crossover point and output a first band signal, the at least one detector configured to measure the radiance in a second band having wavelengths in a spectral band on a second opposing side of the crossover point and output a second band signal; and a data processing unit configured to use the radiance measurements of the road in the first and second bands to determine a radiance ratio of the radiance in the first band and the radiance in the second band and compare the radiance ratio to predetermined critical ratios to output a determination signal indicating the presence of water or various types of ice; characterized in that the crossover point is located in the imaginary parts of the indices of refraction of liquid water and ice at 1,47μm, and the location and width of the first and second bands is selected such that measurements with the first er spectral filter that allows radiance in a first band between about 1.400 and 1.450 μm to pass are used to determine the radiance at one side of the crossover point, and measurements with the second spectral filter that allows radiance in a second band between about 1.475 and 1.525 μm to pass are used to determine the radiance at the other side of the crossover point. at least one detector with first and second spectral filters configured to measure radiance of the road in spectral bands adjacent to a crossover point of the imaginary parts of the indices of refraction of liquid water and ice, the at least one detector configured to measure the radiance in a first band having wavelengths in a spectral band on a first side of the crossover point and output a first band signal, the at least one detector configured to measure the radiance in a second band having wavelengths in a spectral band on a second opposing side of the crossover point and output a second band signal; and a data processing unit configured to use the radiance measurements of the road in the first and second bands to determine a radiance ratio of the radiance in the first band and the radiance in the second band and compare the radiance ratio to predetermined critical ratios to output a determination signal indicating the presence of water or various types of ice; characterized in that the crossover point is located in the imaginary parts of the indices of refraction of liquid water and ice at 1,47μm, and the location and width of the first and second bands is selected such that measurements with the first er spectral filter that allows radiance in a first band between about 1.400 and 1.450 μm to pass are used to determine the radiance at one side of the crossover point, and measurements with the second spectral filter that allows radiance in a second band between about 1.475 and 1.525 μm to pass are used to determine the radiance at the other side of the crossover point. <EOS>