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Venus Express captures images in any light

31 May 2007

ESA's Venus Express is capturing atmospheric details of day and night areas simultaneously thanks to an onboard thermal imaging spectrometer.

A visible and infrared thermal imaging spectrometer (VIRTIS) is helping scientists at ESA to build up what they believe to be the most complete 3D data set of the Venusian atmosphere to date. They hope this information will help them to understand why Venus developed in such a catastrophic way, despite being so similar to Earth.

"Our process allows us to look at the dark and lit sides of Venus' south pole at the same time but we can also look into the atmosphere at different depths," Guiseppe Piccioni, VIRTIS co-principle investigator told optics.org. "It is comparable to looking at bright, sun-illuminated snow and at a dark sky without having to change your glasses."

The VIRTIS combines three unique data channels in one compact instrument. Two are devoted to spectral mapping, housed in the Mapper optical subsystem (VIRTIS-M), while the third is devoted to spectroscopy contained in the high resolution optical subsystem (VIRTIS-H).

"VIRTIS can provide an 'image cube' comprising 256x256 pixels composed of 432 bands in the wavelength range 0.25-5 µm," said Piccioni. "The bands are acquired simultaneously in the detector frame having a direction in the wavelength axis and the other one in the spatial direction."

According to Piccioni, it takes 2.5 seconds to acquire one of the 256 lines that make up each image. This means that a full image is acquired in around 10 minutes.

"We need a very sensitive instrument to detect the radiance coming from below the clouds down to the surface," explained Piccioni. "This radiance is very weak because it is entrapped below the clouds due to the extreme greenhouse effect able to sustain a temperature as high as 450 °C at surface level with a pressure of 92 bar."

VIRTIS-M uses a silicon CCD to produce two-dimensional images in the 0.25-5 µm range and a mercury cadmium telluride infrared focal plane array (IRFPA) to image from 1-5 µm.

The field of view of VIRTIS-H is centered about the middle of VIRTIS-M to provide spectra at high spectral resolution in this portion of the frame. VIRTIS-H employs the same mercury cadmium telluride IRFPA to perform spectroscopy from 2-5 µm.

"We have a lot of work still to come in the next months of observations and data analysis," concluded Piccioni. "We have an observation scheduled for June 5-6th in coordination with the Venus flyby of the Messenger NASA mission to Mercury where we will image the same region and atmospheric features."

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