Sentence:  Observations of the radio emission of a planet which has an extensive atmosphere will probe the atmosphere to a greater extent than those using shorter <WSD>wave</WSD> lengths and should in some cases give otherwise unobtainable information about the characteristics of the solid surface . 
Meaning of the word marked with <WSD> tags:  the distance (measured in the direction of propagation) between two points in the same phase in consecutive cycles of a wave