What does NISTAR see?
NISTAR has a one degree field of view that acts as one large pixel that encompasses the entire sunlit side of the Earth. It has a seven degree field of regard and is aligned with the EPIC camera’s boresight to within 0.1 degrees, so both can simultaneously collect data.
The DSCOVR satellite is in a tilted (Lissajous) orbit about the Lagrangian L-1 point. This point is between the Earth and the Sun, approximately 1.6 million kilometers [1 million miles] from Earth and 150 million kilometers [92 million miles] from the Sun. The Lissajous orbit causes the apparent angular size of the Earth to vary from 0.45 to 0.53 degrees over a 6-month period.
Four broadband channels
The NISTAR instrument looks at the outgoing radiation from the Earth in a variety of wavelength ranges, or bands, indicated in the plot above. Band B measures the amount of sun-light directly reflected from the Earth (blue curve). By subtracting the light collected in band A from that of band B it is possible to determine the radiation emitted from the Earth in the infrared (red curve). The reflected solar energy may be further resolved by subtracting band B from band C.
Total radiation – 0.2 µm to 100 µm
This electrical substitution radiometer channel measures the total radiant power in the UV, visible, and infrared wavelengths emerging from Earth.
Total solar reflected – 0.2 µm to 4 µm
This electrical substitution radiometer channel measures the reflected solar radiance in UV, visible, and near infrared wavelengths from Earth.
Near-infrared solar reflected – 0.7 µm to 4 µm
This electrical substitution radiometer channel measures the reflected near infrared solar radiation from Earth.
Photodiode – 0.2 µm to 1.1 µm
The primary function of this channel is to track the stability of the filters, and to verify co-alignment of NISTAR and EPIC.