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PACE Focus Areas By Wavelength

Orbiting high above Earth's surface, PACE's Ocean Color Instrument (OCI) will measure the radiance, or flux of light emitted, from the top of the atmosphere. The exceptionally broad range of wavelengths sensed by the OCI – from ultraviolet to near-infrared along with several shortwave infrared bands – will support investigation of the ocean, atmosphere, and key climate-related factors. Below are a few examples of science topics that will be investigated using data acquired at various PACE wavelengths.

Tiny particles suspended in the atmosphere (aerosols)

The OCI will sense shorter ultraviolet (UV) wavelengths to reveal information about tiny particles suspended in the atmosphere such as dust and soot, known as aerosols. These particles can be solid or liquid, affecting climate, weather, and people's health. Of keen interest is whether aerosols come from natural sources or are produced by human activities. Data from the visible portion of the electromagnetic spectrum are helpful in determining the sources of aerosols.

Organic material dissolved in water

UV wavelengths will also improve scientists' ability to distinguish dissolved organic material from chlorophyll in the upper ocean. This unprecedented capability will help scientists better understand how much carbon sinks out of surface waters to the deep ocean for long-term storage. The downward transport of organic material is a key process in Earth's carbon cycle and both affects, and is affected by, climate change.

Phytoplankton community composition

The blue portion of the visible spectrum will be used to understand microscopic marine algae forming the base of the marine food web, phytoplankton. Each with its own unique impact on the optical properties of seawater, phytoplankton vary greatly in function, response to ecosystem changes, and nutritional value for their predators. OCI measurements of phytoplankton community composition will be essential for understanding how living marine resources are responding to Earth’s changing climate.

Particle size in the atmosphere and ocean

The green portion of the visible spectrum will be used to determine the size of particles in both the atmosphere and ocean. In the atmosphere, sources of aerosols will be inferred from location and particle size. Natural aerosols, such as dust and sea salts, tend to be larger than man-made aerosols such as smoke and industrial pollution. Phytoplankton and other marine particles also vary greatly in size and thus absorb and scatter light differently, leading to variations in ocean color.

Phytoplankton health

The OCI's enhanced resolution in the visible spectrum, including yellow and orange wavelengths, will reveal additional information on phytoplankton health and physiology. For example, a lack of key nutrients can impact phytoplankton growth rates, pigments, and photosynthetic efficiency. PACE scientists will closely monitor phytoplankton distributions, enabling society to prepare for environmental disruptions such as harmful algal blooms or the collapse of fisheries during El Niño events.

Pigments within phytoplankton

Phytoplankton use pigments such as chlorophyll to harvest sunlight and carry out photosynthesis. The OCI will collect information from across the electromagnetic spectrum — known as "hyperspectral" imaging — giving scientists the ability to observe the fluorescence of various pigments within phytoplankton. This information will be used to distinguish phytoplankton community composition, shedding light on these tiny organisms who make huge contributions to Earth's climate.

Coastal biology

The longest wavelengths within the visible range will be used to study coastal biology. Coastal waters have very different colors than the open ocean, largely because of dissolved or suspended matter in the near-surface water column, which absorb and scatter light in various ways. Scientists will relate variations in coastal ocean color to concentrations of healthy biological constituents and also potentially harmful conditions (e.g., runoff, harmful algal blooms).

Atmospheric clarity over the ocean

Somewhat ironically, short-wave infrared (SWIR) bands are the longest wavelengths that will be measured by PACE. A portion of these will be used to determine the clarity of the atmosphere over the ocean. After removing the contribution based on a clear atmosphere — known as "clear atmospheric correction" — the remaining radiance will be the small portion that has passed through the ocean surface. This "leftover" component of radiance will be a key ingredient in determining the near-surface concentration of chlorophyll.

Coastal atmospheric conditions

Like clear ocean atmospheric corrections, SWIR data from coastal regions will be used to improve PACE algorithms, aiding coastal biology studies. Moreover, the OCI's data on coastal atmospheric conditions will provide valuable information about the distribution and characteristics of clouds. Playing a major part in the balance of energy that enters and leaves the climate system, clouds are one of the biggest sources of uncertainty in computer models that predict future climate. Earth Observatory

Thickness of aerosols

SWIR bands will be used to investigate aerosols, another area of great uncertainty in scientists' efforts to understand Earth's climate system. Aerosol optical thickness is a measure of how much sunlight these airborne particles prevent from traveling through the atmosphere. Depending upon their size, type, and location, aerosols can either cool Earth's surface or warm it. They can help clouds to form or they can inhibit cloud formation. Earth Observatory