数据说明
Sea Surface Salinity (SSS) from SMAP
上传时间：2019-05-22 14:11:09 浏览次数：作者与来源：admin
Sea surface salinity (SSS) is the water salinity close to the ocean's surface. The exact meaning of surface varies according to the measurement method used, generally, it is about 3 millimeters below the sea surface. Psu (Practical salinity units) is the unit of SSS, it represents the amount of salt dissolved in every kilogram (roughly one liter by volume) of seawater.
Unit: psu
Resolution: 0.25 degree, monthly
Duration: Apr 2015 – present
Source: Remote Sensing System
Version: V2.0
Processing: Original monthly mean products are shown.
SMAP is building upon the legacy of Aquarius mission in delivering sea surface salinity (SSS) observations for the world’s oceans. With the loss of the Aquarius mission on June 7, 2015 it became critical also to continue the time series of global salinity observations important to studies of the earth’s water cycle. monthly gridded product is based on the first release of the validated standard mapped sea surface salinity (SSS) data from the NASA Soil Moisture Active Passive (SMAP) observatory, produced operationally by Remote Sensing Systems (RSS) with a one-month latency. Monthly data files for this product are averages over one-month time intervals. SMAP data begins on April 1, 2015 and is ongoing, with a one-month latency in processing and availability. L3 products are global in extent and gridded at 0.25degree x 0.25degree with an approximate spatial resolution of 40km. The SMAP satellite is in a near-polar orbit at an inclination of 98 degrees and an altitude of 685 km. It has an ascending node time of 6 pm and is sun-synchronous. With its 1000km swath, SMAP achieves global coverage in approximately 3 days, but has an exact orbit repeat cycle of 8 days.
The salinity retrieval algorithm retrieves the salinity and wind simultaneously by finding the best fit solution to minimize the difference between the Aquarius data and the model functions：
Cap(w,Φ,SSS)=∑p=V,H(TBp-TBpm)2/ΔT2+ ∑p=W,HH(σ0p-σ0pm)2/(γpσ0p)2+(w-wNCEP)2/Δw2+sin2((Φ-ΦNCEP)/2)/δ2
The weighting factors for the Aquarius data are set according to the expected measurement and modeling uncertainties. We let ΔT be the Noise‐Equivalent‐Delta‐T (NEDT) of radiometer and γp be1.4 times of the radar measurement sensitivity (kpc). The values of NEDT and kpc, a function of signal‐to‐noise ratio, have been precomputed and saved in the Aquarius L2 data files. The value of Δw is 1.5 m s−1, a rather weak constraint because the accuracy of wind speeds is estimated to be about 0.7 m s−1. The value of δ is 0.2, which will constrain the wind direction to be within an RMS deviation of 11° from the NCEP wind direction.
Note that the salinity retrieval algorithm consists of a number of steps that are intended to remove the unwanted sources of radiation (galaxy, sun, moon, and Earth’s atmosphere) in order to obtain just the Earth’s surface emission term.
Known issues
The retrieved data somewhere near continents may be discarded.
Quality of the dataset is highest in open ocean area, and will fluctuate in other places.
All the contents of this page are quoted from Barcelona Expert Centre, National Aeronautics and Space Agency.All project documentation and related publications can be found at website: https://podaac.jpl.nasa.gov/SMAP
Unit: psu
Resolution: 0.25 degree, monthly
Duration: Apr 2015 – present
Source: Remote Sensing System
Version: V2.0
Processing: Original monthly mean products are shown.
SMAP is building upon the legacy of Aquarius mission in delivering sea surface salinity (SSS) observations for the world’s oceans. With the loss of the Aquarius mission on June 7, 2015 it became critical also to continue the time series of global salinity observations important to studies of the earth’s water cycle. monthly gridded product is based on the first release of the validated standard mapped sea surface salinity (SSS) data from the NASA Soil Moisture Active Passive (SMAP) observatory, produced operationally by Remote Sensing Systems (RSS) with a one-month latency. Monthly data files for this product are averages over one-month time intervals. SMAP data begins on April 1, 2015 and is ongoing, with a one-month latency in processing and availability. L3 products are global in extent and gridded at 0.25degree x 0.25degree with an approximate spatial resolution of 40km. The SMAP satellite is in a near-polar orbit at an inclination of 98 degrees and an altitude of 685 km. It has an ascending node time of 6 pm and is sun-synchronous. With its 1000km swath, SMAP achieves global coverage in approximately 3 days, but has an exact orbit repeat cycle of 8 days.
The salinity retrieval algorithm retrieves the salinity and wind simultaneously by finding the best fit solution to minimize the difference between the Aquarius data and the model functions：
Cap(w,Φ,SSS)=∑p=V,H(TBp-TBpm)2/ΔT2+ ∑p=W,HH(σ0p-σ0pm)2/(γpσ0p)2+(w-wNCEP)2/Δw2+sin2((Φ-ΦNCEP)/2)/δ2
The weighting factors for the Aquarius data are set according to the expected measurement and modeling uncertainties. We let ΔT be the Noise‐Equivalent‐Delta‐T (NEDT) of radiometer and γp be1.4 times of the radar measurement sensitivity (kpc). The values of NEDT and kpc, a function of signal‐to‐noise ratio, have been precomputed and saved in the Aquarius L2 data files. The value of Δw is 1.5 m s−1, a rather weak constraint because the accuracy of wind speeds is estimated to be about 0.7 m s−1. The value of δ is 0.2, which will constrain the wind direction to be within an RMS deviation of 11° from the NCEP wind direction.
Note that the salinity retrieval algorithm consists of a number of steps that are intended to remove the unwanted sources of radiation (galaxy, sun, moon, and Earth’s atmosphere) in order to obtain just the Earth’s surface emission term.
Known issues
The retrieved data somewhere near continents may be discarded.
Quality of the dataset is highest in open ocean area, and will fluctuate in other places.
All the contents of this page are quoted from Barcelona Expert Centre, National Aeronautics and Space Agency.All project documentation and related publications can be found at website: https://podaac.jpl.nasa.gov/SMAP
