We have to detect vibration/sound produced at rail track for upcoming train at 1000 m distances . So which sensor is appropriate here? thanks.
If you want to detect sound, use a microphone. If you want to detect vibration, there are a few options, but probably the default option would be a piezoelectric accelerometer. For both microphones and accelerometers, there are thousands of models available depending on the frequency and amplitude range you care about. Cost will be in the hundreds of US dollars range.
If you can provide more detail about what you need to do, we can give you a better answer.