What is the intensity of terrestrial radiation?
Assuming your question is about how much of the sun's radiation hits the Earth's surface rather than just reaching the edge of the atmosphere ...

The amount of solar radiation that hit's the Earth's surface varies a lot, depending on weather conditions, time of day, day of the year, latitude, altitude, air quality ... It can be anywhere between 0 and ~$1200W/m^2$

There is a standard "full sun" solar intensity which is used as a benchmark for things like photovoltaics testing and calibration. That's $1000W/m^2$, with an atmospheric spectrum denoted by AM1.5