What are the four principal windows (by wavelength interval) open to effective remote sensing from above the atmosphere ? 1) Visible-Near IR ( ); 2) Mid- IR (3 - 5); 3) Thermal IR (8 - 14); 4) Microwave ( ccm).

Remote sensing tutorial; AVRIS spectral channels

Apart from the strong absorption bands in the ultraviolet region ozone (blue) exhibits another, albeit weaker, absorption band, the Chappuis absorption band. This is in the visible part of the solar spectrum. Oxygen has a strong absorption band (black mark) at 0.76 µm which will be used in the future to more accurately infer the cloud top height from remote sensing platforms.

Absorption in this region is shown in a measured atmospheric emission spectrum from 6 to 25 m obtained from the Infrared Interferometer Spectrometer (IRIS) onboard the Nimbus IV satellite. Apart from the absorption bands the envelope of the emission spectrum is similar to the emission spectrum of a black body at a temperature of 290 K.

20   1.5   avenumber

The impact the highly variable atmospheric water vapor is presented by the red areas in the figure. The vertical integrated column water vapor content, called precipitable water, ranges for a dry and humid atmosphere between 0.5 cm to 5 cm. The turquoise marked area shows the impact of aerosols for the natural range of the aerosol optical depth (0.1 to 0.5). The wavelengths dependence is visible. In comparison to the absorption of gases, aerosol particles have an impact throughout the whole solar spectrum and no selective absorption bands. Furthermore, the reduction of the total direct solar beam due to aerosols at the surface is large and must be included for climate studies.

Water vapor, carbon dioxide and ozone contribute most to the absorption of thermal or terrestrial infrared radiation. Shortwave solar radiation and longwave infrared radiation is mainly absorbed by atmospheric gases such as water vapor, ozone, carbon dioxide, and methane. Nitrogen, oxygen and argon comprise 99.99% of all atmospheric gases. However, in terms of absorption they make much less of a contribution than some of the other gases such as carbon dioxide and water vapor. Radiation absorption in the near-infrared is related to vibrational molecular transitions and in the far-infrared it is related to purely rotational transitions. The spectral region containing the strongest absorption bands is between 2000 and 3000 nm. These are called Hartley bands. These absorption bands and the adjacent weaker Huggins absorption band are together responsible for very little harmful ultraviolet radiation reaching the earth's surface. Water vapor is the most important absorber in the near infrared region. Carbon dioxide has some weak absorption bands in the solar spectrum.

OC3522Summer 2001 OC Remote Sensing of the Atmosphere and Ocean - Summer 2001 Introduction to Solar Applications

a) Water-Leaving Radiance L w b) Portion of L w reaching satellite c) Portion of L w scattered away d) Sun Glitter e) Sky Glitter f) Portion of L r scattered away g) Portion of L r reaching satellite h) Single-scattered sun rays i) Multi-scattered rays j) Water-leaving radiance scattered into IFOV - not part of L w k) Surface Reflections scattered into IFOV - not part of L r Surface reflections L r h + i + j + k = Atmospheric Path Radiance L p

L T = L p +  a L w +  a L r where  a = Atmospheric Transmittance

SeaWiFS channels: Band Center Wavelength (nm) Bandwidth Band Center Wavelength (nm) Bandwidth (0.412  m) (near IR)

Surface Properties Matter

Atmospheric Properties Matter

The general radiative transfer solution for a scattering atmosphere is: Where the surface radiance (L 0 ) is due to reflection of the downward radiative flux at the surface (read section Kidder & Vonder Haar) The reflection properties of various surfaces can be a complex function of incoming and outgoing directions … commonly called the bidirectional reflectance,  r (  r,  r ;  i,  i ) Common approximations to surface reflectance include: Lambertian or isotropic reflectance Specular or “mirror-like” L 0 =const.  r =  i

The reflection function of ocean water depends on the wind speed. Wind generates waves, foam and air bubbles. The description of these properties goes back to the pioneering work of Cox and Munk in They developed a semi-empirical model describing the rough water surface. It was based on the analysis of sun glint images. They found that the reflection can be best approximated by means of a Gaussian distribution, assuming the wind speed as the only input parameter.

Satellites and Instruments - Visible Applications  TIROS / NOAA Series (polar orbiting; POES (Polar Orbiting Environmental Satellites) * AVHRR (Advanced Very High Resolution Radiometer)AVHRR  m  DMSP (Defense Meteorological Satellite Program - polar orbiting)DMSP * OLS (Optical Linescan System) ~0.4--> 1.1  m (1 channel - broad band)  SeaStar (polar orbiting, sun synchronous NASA) * SeaWiFS (Sea-viewing Wide Field-of-view Sensor)SeaWiFS 8 Visible bands 0.4  m --> 0.8  m  GOES (Geostationary Operational Environmental Satellites NOAA)GOES * I-M series Imager 0.65  m  Terra