ICESat-2 carries a single instrument – the Advanced Topographic Laser Altimeter System, or ATLAS. Like the altimeter on the first ICESat mission, ATLAS measures the travel times of laser pulses to calculate the distance between the spacecraft and Earth’s surface. ATLAS features new technologies that allow it to collect a more detailed, precise picture of the heights of the planet’s ice, vegetation, land surface, water and clouds. As it orbits over the poles, ATLAS has three major tasks: Send pulses of laser light to the ground, collect the returning photons in a telescope, and record the photon travel time.