April 2, 2015

MADRAS and SAPHIR images after geometry correction

level 1A processing

MADRAS et SAPHIR instruments raw data have been processed, with CNES/CLS tools, on one orbit (orbit N° 187) to generate an example of level 1 product.

Here is a quicklook illustrating all the measurements over MADRAS 9 channels

Here is a quick look illustrating all the measurements over MADRAS 9 channels

The data are geolocated. The brightness temperature have been computed for each point of the swath. From left to right, can be seen, on low frequency channels, Africa with Madagascar, Australia, Central America, then West Africa.

The same information has been transfered on the worldmap

 Orbit 187
Brightness temperature on MADRAS 9 channels: Orbit 187

The brightness temperature measured by the satellite depends on:

  • the emissivity of the Earth's surface which varies depending on the nature of the Earth or ocean surface, the nature of the ground, the vegetation, etc...
  • the atmosphere's characteristics over its depth.

The atmosphere lessens the Earth's emissions in a variable way depending on the frequencies:

  • MADRAS low frequency channels (18.7 GHz) actually show the Earth's surface because the atmosphere lessening is low. With an observation incidence of 53°, one notices that the signal is statistically higher in V polarization than in H polarization.
  • The 23.8 GHz channel returns the integrated content in water vapor.
  • The 36.5 GHz channels are more representative of the lower layers of the atmosphere.
  • The 89 GHz channels have a better resolution (around 10 km) than the previous ones and allow to identify the clouds content in volume
  • The 157 GHz channels mainly observe the upper layers of the atmosphere and allow to detect the ice at the cloud tops.

For each channel, data have been transfered on a map for a better visualisation of the satellite track.

On this orbit, a cyclone was forming in the Central America region, a zoom was realised for all the frequencies.

Remark: the color scales are different for each channel

Channel 18,7 GHz – H Polarization
Channel 18,7 GHz – H Polarization
Channel 18,7 GHz – V Polarization
Channel 18,7 GHz – V Polarization
 Channel 23,8 GHz – V Polarization
Channel 23,8 GHz – V Polarization
Channel36,5 GHz – H Polarization
Channel36,5 GHz – H Polarization
Channel 36,5 GHz – V Polarization
Channel 36,5 GHz – V Polarization
Channel 89,0 GHz – H Polarization
Channel 89,0 GHz – H Polarization
Channel 89,0 GHz – V Polarization
Channel 89,0 GHz – V Polarization
Channel 157 GHz – H Polarization
Channel 157 GHz – H Polarization
Channel 157 GHz – V Polarization
Channel 157 GHz – V Polarization

For the same orbit N°187, quicklook showing SAPHIR measurements for the 6 channels

For the same orbit N°187, quicklook showing SAPHIR measurements for the 6 channels

SAPHIR is a sounding instrument measuring the atmosphere brightness temperature (emissivity) in frequency bands located in the water vapor absorption line.

The different channels are thus sensitive to the water vapor content in each of the 6 sub-layers of the atmosphere depending on the proximity of the channel frequency with the water vapor absorption one (183.31 GHz).

Thus Channel 1 only observes the upper part of the atmosphere (about 12 Km above the surface) while Channel 6 measures the radiation emitted by all the atmosphere down to the ground, while being more sensitive to the lower layer of the atmosphere (<5 km).

In the same way, data were transfered on a map and a zoom was realised on the Central America cyclone.

Channel 1 de SAPHIR
Channel 1 de SAPHIR
Channel 2 de SAPHIR
Channel 2 de SAPHIR
Channel 3 de SAPHIR
Channel 3 de SAPHIR
Channel 4 de SAPHIR
Channel 4 de SAPHIR
Channel 5 de SAPHIR
Channel 5 de SAPHIR
Channel 6 de SAPHIR
Channel 6 de SAPHIR

Notice that MADRAS 157 GHz channels and SAPHIT Channel 6 (183 GHz ± 11 Ghz) give well correlated information.

Channel 157 GHz – H Polarization
Channel 157 GHz – H Polarization
Channel 6 de SAPHIR
Channel 6 de SAPHIR