How NASA Is Using Moonlight To Improve Accuracy Of Satellites Observing Earth

Researchers are using reflected moonlight to improve the accuracy of satellites observing Earth. The Moon is extremely stable and not influenced by factors in Earth like climate to any large degree.

New Delhi: Researchers are using reflected moonlight to improve the accuracy of measurements from satellites observing Earth. 

From March 12 to March 16, 2022, NASA's airborne Lunar Spectral Irradiance, or air-LUSI, flew aboard NASA's ER-2 aircraft to accurately measure the amount of light reflected off the Moon.

Kevin Turpie, air-LUSI's principal investigator, said the Moon is extremely stable and not influenced by factors in Earth like climate to any large degree, according to a statement issued by NASA. He said that the Moon becomes a very good calibration reference, using which researchers can set their instruments and see what is happening on Earth.

NASA makes comprehensive satellite calibration and validation efforts, and the air-LUSI flights are part of these efforts. 

How Moonlight Improves Accuracy Of Satellites

With the help of NASA's Earth-observing satellites, researchers get a global perspective on the interconnected Earth system. Many of these satellites measure light waves reflected, scattered, absorbed, or emitted by Earth's surface, water, and atmosphere. The light includes visible light, ultraviolet and infrared wavelengths, and all wavelengths in between.

The individual satellite instruments need to be "in tune" with each other, like musical instruments in an orchestra, for researchers to obtain maximum information. Scientists can use the Moon as a "tuning fork" to easily compare data from different satellites to look at global changes over long periods of time, the statement said.

How air-LUSI Telescope & ER-2 Aircraft Work

The air-LUSI telescope measures how much light is reflected off the lunar surface to assess the amount of energy Earth-observing satellites receive from moonlight. 

The air-LUSI telescope was mounted aboard the ER-2 aircraft managed by NASA's Armstrong Flight Research Center in Palmdale, California.

The ER-2 is a high-altitude aircraft which flies at 70,000 feet, above 95 per cent of the atmosphere, and can scatter or absorb the reflected sunlight. As a result, the air-LUSI telescope could collect very accurate measurements that are analogous to those a satellite would make from orbit. The air-LUSI telescope measured the Moon for four nights just before a full Moon, during the March flights.

Due to this airborne approach, scientists can study moonlight during different phases of the Moon and can also bring the instrument back between flights for evaluation, maintenance, and repair, the statement said.

The air-LUSI spectrometer is constantly at sea level temperature and pressure as it is hermetically sealed. A spectrometer is a device used for measuring wavelengths of light over a wide range of the electromagnetic spectrum. It is typically used to measure wavelengths of electromagnetic radiation that has interacted with a sample.

The telescope collects light, which enters an integrating sphere. After this, the light is directed to the spectrophotometer.

In November 2019, the air-LUSI telescope flew in similar flights. 

According to the researchers, Earth-observing satellite data in the ultraviolet to near-infrared range can be made more consistent by using the data from 2019 and 2022 together.

The aim of NASA's upcoming Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission is to use the Moon as a common benchmark to make its observations more accurate and inter-consistent with other satellite measurements of Earth. 

Turpie said that scientists can take extensively more accurate measurements of Earth using current and future space-borne observatories, once air-LUSI measurements are used to improve the accuracy of the total amount of light coming from the Moon.