HARP2 is a wide field-of-view pushbroom polarimeter with four spectral channels blue (440 nm), green (550 nm), red (665 nm), and near-infrared/NIR (865 nm) measuring the linear Stokes Parameters

Using a “division of amplitude” technique, HARP2 simultaneously captures images in 3 states of polarization. Its image array is divided into spectral “view sectors” which designate up to 60 view angles HARP2 uses to view the Earth.

Data from the HARP2 optical path enters 3 separate detectors which have a structure as shown here.

See HARP2 during the PACE launch  by NASA!

HARP2 as visible on the PACE spacecraft during separation at launch, February 2024.

HARP2 Global Map (Nadir View)


HARP2 Global Map (Backward View)



This image was collected over the west coast of South America showing a patch of stratiform clouds. The true color image is just like we see with our eyes and show regular clouds over the ocean and land surfaces. The polarization image shows a completely different picture, showing the power of the polarization measurements, unique to PACE. The polarization data reviews the colorful cloudbow, a rainbow produced by solar light reflected by cloud droplets (instead of rain drops). The cloudbow contains unique information about the microphysics of the cloud droplets allowing us to measure their sizes, and how they respond to man made pollution and other aerosols. The polarization data from PACE provides microphysical information by aerosol and cloud particles that is not available by any other measurements.