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license: mit |
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tags: |
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- climate |
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- cloud |
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- physics |
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- meteorology |
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- satellite |
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pretty_name: Cloud-Temperature correlation Data |
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size_categories: |
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- 100K<n<1M |
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# Why was it made? |
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- It was made by collocating data from two satellites, INSAT-3DR and CLOUDSAT, dedicated for meteorology. |
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- INSAT-3DR is a geostationary satellite over Indian region, while CLOUDSAT is a polar satellite dedicated for precise cloud observation. |
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- Since CLOUDSAT is a polar satellite (altitude 450 KM), it can only look at one minute region at a time. But because of this we get precise cloud data (Cloudy-Clear distinction, Cloud Height and Cloud Thickness). |
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- Since INSAT-3DR is a geostationary satellite (36,000 KM), it scans almost half of the globe every 30 minutes, with two pixel sizes (4KM × 4KM, and 1KM × 1KM). |
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- Idea is to combine the power of both to approximate cloud data almost anywhere on earth at any given time. |
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# How was it made? |
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- INSAT-3DR (L1B) data and CLOUDSAT (2B-CLDCLASS-LIDAR) data were collected for the whole year of 2017 and collocated to get this final collocated dataset. |
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- Collocation was done by taking readings from both satellites if their pixels were close to each other in both space (<= 4KM) and time (15 minutes). |
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# Etymology and Information |
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- BT (Brightness Temperature) - Measured in Kelvin, it's a measure of how hot a particular object is in a particular wavelength range. The lower the BT, the cooler the emission in that specific wavelength range. |
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- VIS - Visible Region (0.55-0.75 µm). From this reading, Albedo is derived. |
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- SWIR - Short Wave Infrared Region (1.55-1.70 µm). From this reading, radiance is derived. |
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- MIR - Midwave Infrared Region (3.80-4.00 µm) |
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- TIR1 - Thermal Infrared 1 Region (10.3-11.3 µm) |
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- TIR2 - Thermal Infrared 2 Region (11.5-12.5 µm). From all the last 3 reading, brightness temperatures are derived. |
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- The Brightness Temperature measured by satellites is the brightness temperature from the uppermost layer of the pixel. So if a pixel has clouds, its uppermost layer will be at an altitude (say 2-3 km from ground), thus lowering its Brightness Temperature as compared to a cloudless pixel. |
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- Albedo - Fraction of the incident reflected by an object. Always less than 1. In general, if a pixel has clouds, it'll have higher albedo because of cloud's reflective properties. |
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- Thickness - The total thickness of all cloud layers in a particular pixel. For example, if a pixel has 3 distinct cloud layers (1 km thick each), the total cloud thickness would be 3 km. This doesn't take the cloud's optical density into account, so caution is advised. |
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- InsatCorTir - Coordinates of INSAT pixel's TIR1/TIR2 system. |
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- InsatCorVis - Coordinates of INSAT pixel's VIS system. |
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- CsatCorTir - Coordinates of Cloudsat's pixel that was used to collocate with InsatCorTir. The distance between InsatCorTis and CsatCorVis is VisOffset. |
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- CsatCorVis - Coordinates of Cloudsat's pixel that was used to collocate with InsatCorVis. The distance between InsatCorVis and CsatCorTir is TirOffset. The lesser the offsets, the more reliable the readings. |
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- LandSeaFlag - 1- Land, 2-Ocean, 3-Coast |
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- SolarElevation - 90 degrees when sun is overhead, 0 when sun is rising or setting. |
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- SatElevation - 0 degree when satellite is overhead. ± 90 degrees when satellite is on the horizon. |
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- Elevation - Height above Sea Level. -9999 indicates ocean. 9999 indicates error in height calculation. |
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- Profile - A profile is equivalent to one pixel for CLOUDSAT. In one orbit, it makes approximately 40K profiles, accounting to a length of 1.12KM/profile along the satellite's orbit. Profile number is just the number of profile, starting from 0 when CLOUDSAT starts a new orbit. |
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- Orbit - Total number of orbits completed by CLOUDSAT at that time. |
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- A single slice of atmosphere of length and breadth 1 KM, can have at max 5 separate cloud layers. It is very rare to have more layers than that, although not impossible. So CLOUDSAT is designed to measure data of 5 cloud layers only. |
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- c1type, c2type, c3type, c4type, c5type - Types of clouds in 1st, 2nd, 3rd, 4th and 5th cloud layer. |
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- cloud base height, top height are the height of cloud base and cloud top from the ground. Thus for any given cloud, top height > base height. |
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- All times are GST based. Time = 415 means, 04:15AM GST. Local time can be derived by using any of the coordinates. |
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# What is the purpose of the dataset? |
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- It can be used to evaluate cloud-data (cloudy/clear distinction, cloud top height etc.) from brightness temperatures. Brightness temperatures are readily available to us every 30 minutes. |
