Cloud top pressure/altezza1. Temperatura Necessita il profilo, giorno/notte, emissivita’2. Temperatura corretta Necessita il profilo, stima optical thickness,
relazione optical thickness emissivita’3. A partire dal tipo (soggettiva e storica)4. Ombra (illuminazione, cloud detection, shadow detection, calcolo). Solo di
giorno, sole allo zenith, solo bordi, no calibrazione, si risoluzione spaziale (OK per VIS), complessita’ nel riconoscimento di forme, solo su superfici riflettenti, nubi fine e senza contorni definiti (cirri)
5. Stereoscopia. >1 osservazione contemporanee (vento) (geostazionari: perfettamente in fase, multiviewing: (A)ATSR (2), MISR (9), POLDER (14)), geometria (no calibrazione), cloud detection, navigazione, cloud recognition (difficile, limitato ai bordi), risoluzione spaziale, nubi fini e senza contorni
6. Limb sounding + vede nubi fine, no calibrazione, problemi a scendere (<7 km), possibilie ambiguità con aerosols, numero di misure per orbita, risoluzione spaziale (cirri sono estesi)
7. CO2 slicing8. MLEV (minimum local emissivity radiance)9. WV intercept method10. Molecolar scattering (Raman scattering)11. A-band assorbimento. Photon path length, solo giorno12. Lidar13. Cloud radar
OMBRA
http://www-research.ge.ucl.ac.uk/cloudmap/reports/firstreport.pdf
Stereoscopia
Stereoscopia
Hasler, BAMS 1981
Hasler, BAMS 1981
Hasler, BAMS 1981
IR-WVCurva precalcolataMisura clear skyMisura broken cloudyStima Tb fully cloudy
MLEV
CO2Slicing
InputTemperature and Water Vapor profiles
(representative of the FOV under consideration)
Observations for, at least, two channels in the CO
2 absorption band
CO2Slicing: Theory
Solving Equation:
Iob()-Iclear()
Iob()-Iclear()
Icloud(,pc)-Iclear()
Icloud(pc)-Iclear()
=
The solution is given by the value of pc that minimizes the difference
between the right and left side
Pair Selection
Broad Band Spectrometer:Interferometer:
Example spectra
CO2Slicing: weighting function
spaceMODIS
CO2 channels
Interferometer CO
2 channels
IR Retrieval Scheme for Clouds
Temperature andwater vapor
retrievalsin clear sky
FOVs
Calibrateddata
Cloud mask
Determinationof cloud altitude,
thickness and temperature
Determinationof cloud
emissivityRetrieval of
microphysical properties (optical
thickness, ice water path,
particle size and shape)
Validation of Products
Cloud Emissivity
observed clear
cloud clear
I IN
I I
I
I I
I I
I I I II
I
I Iclear
cloud
clear cloud clearclear
cloud
clear cloud( ) ( )( ) ( )
I
I I
I I
I I I II
I
I Iclear
cloud
clear cloud clearclear
cloud
clear cloud( ) ( )( ) ( )
Minimum Local Emissivity Variance (MLEV)
Observations between 750 and 900 cm-1
2'' min
observed clear
cloud clear
I I
I I
Retrieved cloud at 9.5 km, lidar indicates single layer cloud between 7.5 and 9.8 km.
lidar
The fact that the depth of solar Fraunhofer lines in scattered light is less than those observed in direct sunlight, was discovered by Shefov [1959] [17] and Grainger and Ring [1962] [6] and is known as the ”Ring Effect” or ”Filling-in”. Several publications analysed this effect and its origins, showing that rotational Raman scattering provides the dominant contribution to the Ring Effect [1, 10, 4, 5, 8, 3, 18]. The majority of these studies however concentrated on cloud-free conditions.
Cloud radar
• INIZIO VECCHIE: VERIFICARE
Cloud top pressure, temperature, effective emissivity Retrieved for every 5x5 box of 1 km FOV’s, when at least 5
FOV’s are cloudy, day & night CO2 Slicing technique (5 bands, 12.0-14.2 µm)
– retrieve pc; Tc from temperature profile
– ratio of cloud forcing in 2 nearby bands– most accurate for high and mid-level clouds
Previously applied to HIRS (NOAA POES, 20 km), GOES sounder (~ 30 km)
Accuracy of technique ~ 50 mb
MODIS 1st satellite sensor capable of CO2 slicingat high spatial resolution
Cloud top properties ((P. Menzel, R. Frey, K. Strabala, L. Gumley, et al. – P. Menzel, R. Frey, K. Strabala, L. Gumley, et al. –
NOAA NESDIS, U. Wisc./CIMSSNOAA NESDIS, U. Wisc./CIMSS))
S. Platnick, ISSAOS ‘02
CO2 slicing: theory
Solving Equation:
Iob()-Iclear()
Iob()-Iclear()
Icloud(,pc)-Iclear()
Icloud(pc)-Iclear()
=
solution given by the value of pc that minimizes the difference
between the right and left side
CO2slicing: weighting functions
Bands w/greater CO2 absorptionhave weighting functions more
sensitive to high clouds
S. Platnick, ISSAOS ‘02Example spectra (~ 12.65-14 µm)
MODIS CO2 band weighting functions
1000
100
10
0.0 0.2 0.4 0.6 0.8 1.0
Pre
ssu
re (
mb
)
Weighting Function dt(,p)/d ln p
Channel 32 33 34 35 36
Central Wavelength (µm)
12.020 13.335 13.635 13.935 14.235
36
1.2
35
34
33
321000
100
10
0.0 0.2 0.4 0.6 0.8 1.0
Pre
ssu
re (
mb
)
Weighting Function dt(,p)/d ln p
Channel 32 33 34 35 36
Central Wavelength (µm)
12.020 13.335 13.635 13.935 14.235
36
1.2
35
34
33
32
BT in and out of clouds for MODIS CO2 bands
- demonstrate weighting functions and cloud top algorithm
S. Platnick, ISSAOS ‘02