Can I do refraction on pavement? It is exceedingly difficult to do this, because the pavement is generally has a much higher velocity that the materials below it. It is generally not recommended.
Can I do refraction on a hillside? Yes. The slope of the surface is not relevant (at least in theory, although there may be obviously practical limits).
Can I survey in the rain? Rain won’t hurt the seismographs. If you are using a StrataVisor or SmartSeis and it starts raining, they should be fine as long as they are kept vertical, with the screen pointing up. But acquiring data in the rain should be avoided, especially if there is lightning. Even in the absence of lightening, rain can be a significant source of noise, especially those raindrops striking the geophones directly. Obviously, the harder the rain, the more noise. If waiting the rain out is impractical, shielding the geophones themselves can reduce the noise significantly. If for some reason the seismic system must be left on the ground during an electrical storm, it is advisable to disconnect the trigger and geophone cables from the seismograph.