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Sentinel 5P: Suomi-NPP VIIRS cloud level 2 data

Status: Ongoing
Online Status: ONLINE
Publication State: Preview
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Sentinel 5 Precursor (S5P) was launched on the 13th October 2017 carrying the TROPOspheric Monitoring Instrument (TROPOMI). The TROPOMI instrument onboard Sentinel-5 Precursor (S5P) is a nadir-viewing, imaging spectrometer covering wavelength bands between the ultraviolet and the shortwave infrared. The instrument uses passive remote sensing techniques to attain its objective by measuring, at the Top Of Atmosphere (TOA), the solar radiation reflected by and radiated from the earth.

The S5P level 2 methane product is dependent on having information on cloud occurrence at spatial resolution finer than that achievable from TROPOMI itself. This information is also useful for other purposes, including assessing the influence of cloud on other L2 products and issues related to spatial co-registration. A level 2 auxiliary product was therefore developed to describe cloud in the TROPOMI field of view (FOV), using co-located observations of VIIRS (Visible Infra-red Imaging Radiometer Suite) on the U.S. S-NPP (Suomi - National Polar-orbiting Partnership). S5P flies in a so-called loose formation with the S-NPP with a temporal separation between them of less than 5 minutes.

The main information contained in the S5P-NPP product is:

1. A statistical summary for each S5P FOV of the NPP-VIIRS L2 Cloud Mask (VCM).
2. The mean and standard deviation of the sun-normalised radiance in a number of VIIRS moderate resolution bands.
This information is provided for three S5P spectral bands (to account for differences in spatial sampling).

The S5P NPP Cloud product contains information on cloud and scene homogeneity for TROPOMI
scenes, derived from operational products from the VIIRS on board the Suomi National Polar-orbiting Partnership (NPP) platform. S5P operates in loose formation orbit with NPP, so that measurements from VIIRS are well co-located with TROPOMI, with a time difference of about 3.5 minutes. There is no specific validation of auxiliary products within the S5P Mission Performance Centre.

Citable as:  [ PROVISIONAL ] Copernicus; European Space Agency (9999): Sentinel 5P: Suomi-NPP VIIRS cloud level 2 data. NERC EDS Centre for Environmental Data Analysis, date of citation.
Abbreviation: Not defined
Keywords: Sentinel, ESA, VIIRS


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Data lineage:

Data collected and prepared by European Space Agency (ESA). Downloaded from the Collaborative Hub for use by CEDA users.

Data Quality:
See dataset associated documentation.
File Format:
These data are in NetCDF format.

Process overview

This dataset was generated by a combination of instruments deployed on platforms and computations as detailed below.

Instrument/Platform pairings

Suomi NPP: Visible Infrared Imaging Radiometer Suite (VIIRS) Deployed on: SNPP

Computation Element: 1

Title Level 2 (L2) cloud retrieval algorithm applied to Suomi National Polar-orbiting Partnership (SNPP) Visible Infra-red Imaging Radiometer Suite (VIIRS) instrument: level 2 Suomi-NPP VIIRS raw cloud data.
Abstract The computation process for the transformation of cloud data from the VIIRS instrument on board the JPSS (Joint Polar Satellite System) operational meterological satellite prototype SNPP, to To view the retrieval algorithms for these products, visit the following Sentinel/Copernicus page: The S5P-NPP Cloud processor is a stand-alone code separate from other TROPOMI-related computations. The retrieval algorithm requires the following input fields: • Semi-major and semi-minor axis, and eccentricity, of the WGS'84 ellipsoid • Time window of tolerance to identify relevant NPP files for a given S5P scan line • Number of VIIRS cloud classifcations, defined S5P FOVs, and VIIRS moderate resolution channels used in the S5P-NPP product • Maximum and minimum values of transformed coordinates (y & z) which define a specific S5P FOV. • Instantaneous spatial response function • Latitude and longitude of S5P pixel corner, centre or sensor, and altitude of sensor • View zenith angle of S5P pixel and line-of-sight zenith angle of a VIIRS pixel • Sensing time of S5P scan line and a VIIRS scan line • Sensing start and stop time of S5P L1 file • Latitude and longitude of VIIRS pixel • Sensing start and stop time of NPP L1 file • Sensing start and stop time of NPP L1 granule • Sensing start and stop centre-scan latitude and longitude of NPP L1 granule • VIIRS pixel level geolocation, radiance and cloud mask data quality flags • VIIRS band averaged spectral radiance • VIIRS pixel cloud mask • Ratio of nominal FOV extent to that of L1GPC in across- and along-track directions • Spatial response function (SRF), including effects of satellite motion The retrieval is performed in 3 steps: 1) S5P L1 file is ingested, containing the geolocation of each scene for which the S5P-NPP-Cloud information is required. 2) The time difference, ∆tsat, between S5P centre-swath observations and those of spatially co-located VIIRS measurements is calculated to an accuracy of ≈1 minute using metadata in the VIIRS geololcation file. 3) S5P scan lines are looped over: a) VIIRS files which contain information relevant to these scan lines are identified b) The relevant information from these VIIRS files is read and stored in memory c) S5P across-track pixels within the current scan line are looped over. The NPP-Cloud product is then the re-gridding of the VIIRS L1 and cloud mask products from the SNPP to the resolution acquired by the TROPOMI instrument on the Sentinel 5P satellite. For more information on the processing algorithm please look at the ATBD (Algorithm Theoretical Baseline Document) on the Sentinel Copernicus webpage, URL linked in the documentation.
Input Description None
Output Description None
Software Reference None
Output Description None

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