Satellite Sensors
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Inter-comparison Database
The evaluation of passive imager cloud properties retrievals is part of CREW. For CREW-2 five Golden days were selected for which the retrievals of the participating algorithms are inter-compared and compared against reference datasets collected by the A-train satellites (Cloudsat, Calipso, AMSR, and MODIS). This comparison will be continued for CREW-3. Below we will provide information that is relevant for those who plan to upload data for the CREW (inter)-comparison activity.
GOLDEN DAYS
We have selected five Golden Days which are listed in Table 1. During part of the selected Golden Days the MODIS on-board Aqua aligned with AVHRR on-board NOAA-17. Our evaluation study will focus on the hours during which both instruments are aligned. However, for those providing SEVIRI or MODIS data datasets covering the full golden days is encouraged.
- SEVIRI full disk data every 15 minutes preferably covering the 24 hrs at the golden days - MODIS swath data over the full disk area of MSG preferably covering the 24 hrs at the golden days - AVHRR swath data over the full disk area of MSG during the hours where NOAA-17 was aligned with Aqua
Table 1 lists the Golden Days that have been selected for the (inter)-comparison.
Table 1: GOLDEN DAYS of CREW-2 & CREW-3
| Day | Month | Year | Period that Aqua and NOAA 17 were aligned |
|---|---|---|---|
| 13 | June | 2008 | 12:00-15:30 |
| 17 | June | 2008 | 22:15-24:00 |
| 18 | June | 2008 | 00:00-01:45 |
| 22 | June | 2008 | 10:30-12:15 |
| 03 | July | 2008 | 10:00-12:00 |
Note: The data sets are stored on the FTP site of ICARE and is available only for CREW members, see Data_Access.
PRODUCTS
Table 2 lists the cloud parameters that are part of the (inter)-comparison of CREW.
Table 2: cloud physical properties
| acronym | property |
|---|---|
| cm | cloud mask |
| cfr | cloud fraction |
| ctt | cloud top temperature |
| ctp | cloud top pressure |
| cth | cloud top height |
| cod | cloud optical depth |
| ref | effective radius |
| lwp | liquid water path |
| iwp | ice water path |
MSG/SEVIRI
SEVIRI is a 50 cm-diameter aperture, line-by-line scanning radiometer, which provides image
data in four Visible and Near-InfraRed (VNIR) channels and eight InfraRed (IR) channels. A
key feature of this imaging instrument (Fig. 1) is its continuous imaging of the Earth in 12
spectral channels with a baseline repeat cycle of 15 min. The imaging sampling distance is
3 km at the sub-satellite point for standard channels, and down to 1 km for the High
Resolution Visible (HRV) channel. (from www.esa.int)
Data access for the CREW periods here:
./crew/observations/SEVIRI
MODIS
MODIS (Moderate-resolution Imaging Spectroradiometer) is a payload scientific instrument launched into Earth orbit by NASA in 1999 on board the Terra (EOS AM) Satellite, and in 2002 on board the Aqua (EOS PM) satellite. The instruments capture data in 36 spectral bands ranging in wavelength from 0.4 µm to 14.4 µm and at varying spatial resolutions (2 bands at 250 m, 5 bands at 500 m and 29 bands at 1 km). Together the instruments image the entire Earth every 1 to 2 days. (from Wikipedia)
Data access for the CREW periods here:
./crew/observations/MODIS
AVHRR
AVHRR instruments measure the reflectance of the Earth in 5 relatively wide (by today's standards) spectral bands. The first two are centered around the red (0.6 micrometer, 0.5 THz) and near-infrared (0.9 micrometer, 0.3 THz) regions, the third one is located around 3.5 micrometer, and the last two sample the thermal radiation emitted by the planet, around 11 and 12 micrometers, respectively. (from Wikipedia).
Data access for the CREW periods here:
./crew/observations/AVHRR
CALIOP
The Cloud-Aerosol LIdar with Orthogonal Polarization (CALIOP) is the primary instrument on the CALIPSO satellite, which was launched in 2005. CALIOP provides profiles of total backscatter at two wavelengths, from which aerosol and cloud profiles will be derived. The instrument also measures the linear depolarization of the backscattered return, allowing discrimination of cloud phase and the identification of the presence of non-spherical aerosols.
Data access for the CREW periods here:
./crew/observations/CALIOP
CPR
AMSR
Synthetic datasets
Simulated satellites scenes can be used to validate retrieval algorithms with a 'know truth'.
Data access for the CREW periods here:
./crew/observations/SYNTHETIC
