The Atmosphere Layers Composition

Composition of “air” - What’s in it? Stable Components: N 2 78% O 2 21% CO 2 < 1% 100%

Variable Components: H 2 O Vapor – highly variable (0 to 4%) O 3 - photochemical reactions

Layers of the Atmosphere  Troposhpere Where we live Weather 90% of total mass of atmosphere

 Stratosphere Contains O 3 Absorbs ________??

 Mesosphere Coldest layer Meteor dust act as cloud nuclei  Thermosphere Warmest layer  Ionosphere Absorbs cosmic rays, gamma rays, x- rays, shortest UV

Effect of Atmosphere on EMR n All solar emr passes through space to reach top of atmosphere, but not all reaches Earth's surface. n Atmosphere scatters, absorbs and reflects a portion of in-coming solar radiation. n Earth scatters, absorbs and reflects solar radiation that gets transmitted through the atmosphere. n Finally - atmosphere scatters, absorbs and reflects the electromagnetic radiation that is reflected off the Earth's surface back toward the sensor.

n Atm. Gases; –Critical to earth's energy balance through absorption and emission. –Determines solar radiation reaching surface n "windows" –atm. effects are minimal –allows ground-based measurements of celestial objects, and satellite-based measurements of earth's surface/atm.

n Signal reaching the sensor may include reflection off Earth's surface that contains information, but it also includes in-coming and reflected EMR that has been scattered by the atmosphere. n This can result in a loss of detail in the resulting images, making interpretation more difficult.

Challenges of Remote Sensing n 4% of in-coming solar radiation is reflected back from Earth's surface. n 5% re-radiated after absorption as thermal IR. n These two components are the focus of most terrestrial remote sensing.

Challenges of Remote Sensing n Only selected wavelengths are able to penetrate Earth's atmosphere and be reflected back to sensor. n Thus, only some wavelengths are available for analysis and some objects of interest may not have unique spectral signatures within the set of available wavelengths.

n Composition of atmosphere is important in understanding the role it plays in remote sensing and in interactions with electromagnetic radiation. –largely a mixture of gases –some with fairly constant concentrations –others are variable in space and time. –In addition - suspended particles (e.g. aerosol, smoke, ash etc.) and hydrometeors (e.g. cloud droplets, raindrops, snow, ice crystals, etc). n About 99% of the mass lies below an altitude of 30km.

Table 1: composition of atmosphere below 100km.

Main gases which absorb radiation. ultraviolet (UV), visible, infrared (IR) and microwave wavelengths. main spectral regions ("windows") for which atmospheric absorption is small, are listed at the bottom of the table.