数据介绍

GRACE（Gravity Recovery and Climate Experiment）是一种新的监测全球水资源变化来反演陆地水变化的方法。

卫星于2002年3月发射，由美国宇航局 (NASA) 和德国空间局 (DLR) 共同研发。 GRACE 由一个相距 220 km 的双星系统组成，其轨道高度为 300~500 km，轨道倾角为 89.5°，通过搭载在卫星上的精密测距系统测量星间距离变化反演全球重力场变化。

GRACE 卫星的数据处理、发布与管理主要由喷气动力实验室 (JPL)、美国德克萨斯大学空间研究中心 (CSR) 和德国波茨坦地学中心 (GFZ) 共同完成。

GRACE 的数据产品主要分为 Level-0、Level-1、Level-2 和 Level-3 等，Level-2 包括 GSM、 GAA、 GAB、 GAC 和 GAD 等数据产品。

• GSM表示大地水准面模型的球谐位系数；
• GAA表示高频大气模型对应的球谐位系数；
• GAB 表示高频海洋模型对应的球谐位系数；
• GAC 表示大气海洋模型对应的球谐位系数(全球)；
• GAD 表示大气海洋模型对应的球谐位系数(海洋)。

数据下载

目前GRACE用于估计陆地水储量变化的数据主要有Mascon，L3和L2（球谐系数）。最新版的GRACE的数据为 RL06 版本。对于初学者，Mascons和L3产品是不错的选择。

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Mascon数据

三家研发单位对应三种产品：

1. 美国德克萨斯大学空间研究中心 (CSR Mascon)

版本为 CSR GRACE/GRACE-FO RL06 Mascon Solutions (version 02)

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Thank you for your interest in the GRACE and GRACE-FO RL06 Mascon solutions from the Center for Space Research. The GRACE and GRACE-FO solution time series are provided as single NetCDF timeseries. The CSR RL06 mascons are available in two formats.

1. The solutions with all the appropriate corrections applied (GAD, GIA, C20, C30, degree1, etc) in equi-angular grids.
   * Seperate components files are also available for advanced users to undo the respective corrections
2. Mascon estimation solutions represented as spherical harmonic coefficients.
   Note: CSR Version 02 Mascon grids are represented on an ellipsoidal Earth unlike the previous versions.

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下载地址
http://www2.csr.utexas.edu/grace/RL06_mascons.html

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2. 喷气动力实验室 (JPL Mascon)

版本为 GRCTellus JPL-Mascons: Data Processing (RL06M.MSCNv02)

• The RL06M.MSCNv02 surface mass change data are based on the Level-1 GRACE/GRACE-FO observations, processed at JPL;
  The C20 (degree 2 order 0) coefficients are replaced with the solutions from Satellite Laser Ranging [Cheng et al., 2011], because the —native GRACE-C20 values have a larger uncertainty than the SLR-values.

• The degree-1 coefficients ( Geocenter) are estimated using the methods from Sun et al., (2016); Swenson, Chambers, and Wahr (2008).
  A glacial isostatic adjustment (GIA) correction has been applied based on the ICE6G-D model from Peltier et al. (2017).

• The JPL-RL06M uses a-priori constraints in space and time to estimate global, monthly gravity fields in terms of equal-area 3x3 spherical cap mass concentration functions to minimize the effect of measurement errors. No additional empirical destriping filter has been applied to the data. This results in better S/N ratios of the mascon fields compared to the conventional spherical-harmonic solutions.

• The data are represented on a ½ degree lon-lat grid, but they represent the 3x3 degree equal-area caps, which is the current native resolution of JPL-RL06M.

• All reported data are anomalies relative to the 2004.0-2009.999 time-mean baseline. Note that this baseline needs to be consistent when comparing GRACE/GRACE-FO data to other anomaly data (e.g., groundwater or sea level). Please check the FAQs regarding questions about the time-mean field.

• Note that the land-grid-scaling (described below) has not yet been applied to the GRACE/GRACE-FO data fields; users must apply these optional gain factors. Note that mascon gain factors are (1) different from the harmonic-based grids, and (2) generally much smaller than those due to the better S/N ratio of the mascon fields.

• For an evaluation of errors / uncertainties, please review Wiese, Landerer and Watkins (2016). Due to the implementation of time correlation in the solution procedure, with the addition of each consecutive month, the gravity estimate of all previous months changes very slightly. The largest changes occurr towards the end of the timeseries (the last ~4 months). To ensure that the best estimate of gravity is provided, we update and re-estimate all previous months as well when a new month is added. Any new solution is self-contained in one netcdf file, which is updated for all months each time a new month is released. We recommend to use the most recent solutions available.

• check out the README for more details on the current release (RL06).

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数据介绍：https://grace.jpl.nasa.gov/data/get-data/jpl_global_mascons/
数据下载：https://podaac.jpl.nasa.gov/GRACE

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3. 戈达德空间飞行中心 (GSFC Mascon)

GSFC提供不同后处理方式的产品，供不同领域的研究使用。
陆地水储量研究可采用：GSFC.glb.200301_201607_v02.4-ICE6G，采用最新的ICE6G GIA改正

关于 GSFC的介绍为
https://earth.gsfc.nasa.gov/geo/

数据介绍及下载：
https://earth.gsfc.nasa.gov/geo/data/grace-mascons
GRACE Mascons - Current Products

Name: GSFC.glb.200204_202009_RL06v1.0_OBP-ICE6GD
Summary: Global mascon solution where the GAD product has been restored, meaning the ocean mascons describe ocean bottom pressure (OBP). This product is comparable to the JPL and CSR mascon products.
Grid: 1-arc-degree equal area cells
Available formats: HDF5, ASCII

Name: GSFC.glb.200204_202009_RL06v1.0_SLA-ICE6GD
Summary: Global mascon solution where the GAD product has been restored and the mean GAD over the ocean has been removed, meaning the ocean mascons describe sea level anomalies (SLA), and their sum captures the mass component of global mean sea level change.
Grid: 1-arc-degree equal area cells
Available formats: HDF5, ASCII -

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L3 数据

L3数据由Landerer and Swenson 于2012年发布，该成果发表在Water Resource Research 杂志上。

Landerer,F.W., Swenson, S.C., 2012. Accuracy of scaled GRACE terrestrial water storage estimates. Water Resour. Res., 48(4). doi:10.1029/2011wr011453

数据介绍：
https://grace.jpl.nasa.gov/data/get-data/monthly-mass-grids-land

下载网址：
https://podaac.jpl.nasa.gov/GRACE

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L2 数据

下载网站：http://icgem.gfz-potsdam.de/series

网站里包含：CSR, JPL, GFZ, ITSG等以及国内中科院测地所，同济大学，武汉大学，华中科技大学，西南交通大学发布的球谐系数数据。

【彩蛋】关于GRACE Level 3的用户手册已经上传至个人资源，需要可自行下载