Interaction of Water Reflectance with Earth

How much of Earth’s surface is covered by water

Approximately 74%

What aspects of water need to be monitored

Water quality, sediment content, oxygen content, temperature, salinity etc, that can provide a valuable prospective at a broad scale

How is EMR incident on water reflected

Unlike vegetation and soil the majority of EMR incident on water are either absorbed or transmitted

Does clear water have a lower or higher reflectance over the visible, NIR, and SWIR regions

Very low reflectance (< 3%)

Does clear water have a lower or higher reflectance over the blue and green wavebands

Higher reflectance

What wavelength does clear water have almost no reflectance

> 0.8 μm

What type of image is useful for masking out water bodies or mapping floods

Near infrared images as they show a sharp contrast between water and land boundary

What are the three types of water reflectance

-Surface reflectance
-Volume reflectance
-Bottom reflectance

What is surface reflectance caused by

Caused by specular reflection, and is responsible for the sun’s glint on the water

What does volume reflectance provide information on

Water quality (related to material in the water) e.g., for deep (> 2 m) clear water bodies, volume reflectance is very low (6-8 %) and is confined to the visible wavelengths

What factors affect the reflectance of water

-Depth of water and substrate below the water

-Material within water, sediment and water chlorophyll content

-Surface roughness of water

What is the correlation between depth and water reflectance

The shallower the water, the more bottom reflectance

What fraction of Earth’s biodiversity live in and around coral reefs

25% of all marine species

Why are coral reefs undergoing rapid changes

-Marine heat waves
-Coastal development
-Resource extraction

How is remote sensing used as a tool to help map coral reefs

-Satellite data and bathymetry used withing a machine learning framework to map coral cover

-Hyperspectral (400 wavebands) imagery to detect presence of live coral

-Investigated drivers of live coral location

What is the correlation between surface roughness and water reflectance

Surface roughness tends to decrease observed reflectance except in areas of sun glint

How can we map surface roughness

-Pollution mapping

-Submarine topography

-Wave formation