An attempt to estimate the Thermal Budget of the Earth from VIRTIS Rosetta images A. Adriani, A. Coradini, F. Oliva IFSI-INAF M. L. Moriconi ISAC-CNR P. Irwin University of Oxford and the VIRTIS team
Work in progress: the state of the art ØComplete review and selection of the suitable observations. ØIdentification and Classification of the images in topical areas. ØComparison between areas in daytime vs nighttime ØPreliminary simulation by radiative transfer code ØComparison between NIMS and VIRTIS observations ØSet-up of the NEMESIS radiative transfer code from Oxford University
Review and selection of the suitable observations
Review and selection of the suitable observations
Identification and Classification of the images in topical areas OCEAN MASK: R 758 < 0. 04 Area where the signature of the ocean has been identified→ Oxygen band at 758 nm→ Ocean Mask ↓
Identification and Classification of the images in topical areas LAND MASK: (R 707 / R 527) ≥ 1. 39 Area where the signature of the land has been identified → Test bands→ Land Mask↓
Identification and Classification of the images in topical areas THICK VEGETATION MASK: (R 713 / R 685) ≥ 1. 18 Area where the signature of the vegetations has been identified → Test bands→ Vegetation Mask↓
Identification and Classification of the images in topical areas CLOUD MASK The cloud mask has been calculated by removing the sea, the land the vegetation from the image. The discrimination between high and low clouds has been done by using the depth of the oxygen 758 -nm band. All cloud mask ↓
Identification and Classification of the images in topical areas LOW CLOUD MASK: R 758 ≤ 0. 138 Area where the signature of the low clouds have been identified → Oxygen band at 758 nm → Low Clouds Mask ↓
Identification and Classification of the images in topical areas HIGH CLOUD MASK: R 758 > 0. 138 Area where the signature of the low clouds have been identified → Oxygen band at 758 nm → High Clouds Mask ↓
Identification and Classification of the images in topical areas Average radiances in the visual region Average radiances in the infrared region
Comparison of the same geographical areas: day vs night The area is: ± 20° latitude and 270/320 longitude The observation angle is 36°± 12° for the daytime region and 25°± 11° for the nighttime region 1. 14 W/m 2/µm/sr 0. 12 I 1 -00216741598 I 1 -00216698499 0. 72 W/m 2/µm/sr 0. 22
Comparison of the same geographical areas: day vs night Average spectral radiances from the area -20/+20 latitude and 270/320 longitude. Spectral comparison from the previously selected and identified areas superimposed on theoretical Planck functions. Standard tropical T & P atmospheric profile used in the preliminary radiative transfer simulation by SBDART web tool is based on the UCSB SBDART code by P. Ricchiazzi et al. , 1998.
Thermal Emissions: Comparison NIMS-VIRTIS NIMS December 1992, 5008 nm VIRTIS October 2009, 5011 nm S S N N I 1 -00216741598
Ocean Thermal Emissions: Comparison NIMS-VIRTIS NIMS sees ± 15° lats, 60°E÷ 100°E longs VIRTIS sees ± 15° lats, 100°W÷ 120°W longs
NEMESIS • • • Non-linear optimal Estimator for Multivariat. E spectral analy. SIS. Non planet-specific. Allows for the simultaneous retrieval of any combination of up to four different continuous variables: 1. 2. 3. 4. • • • Temperature Volume mixing ratio of any IR-active gas Cloud opacity Para-H 2 fraction Nemesis can also determine single parameters such as surface temperature, altitude at a particular pressure level, etc. Nemesis makes full use of the implicit differentiation correlated-k code for non-scattering calculations and finite differencing for scattering calculations. Nemesis has been used to simulate the observed spectra of all the planets in the Solar System, but never before for the Earth.
Progress on NEMESIS Preliminary dayside calculation • K-tables for Rosetta wavelength Range computed from HITRAN linedata. • Initial Nemesis calculations are reasonably representative. • Visiting student currently working on cube provided by Alberto Adriani and Maria Luisa Moriconi to compare with work done in Rome. • Hope to then retrieve atmospheric properties over wide areas.
Conclusions ØThe calculation of the Earth thermal budget is not so straightforward because of the limited coverage of the observations. ØAnother issue is the limited spectral interval available which is sometimes even more limited buy the fact that some measurements are saturated beyond 4. 5 μm ØThe extrapolation of the observations done in limited area to the planet will attempted but the goodness of this approach has to be carefully evaluated. ØThe use of radiative transfer simulations can help on this matter.
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