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MODIS Water Vapor & PWC

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UNRESTRICTED

This data set is only available for a restricted user group, please contact us if you want to access these data.

RESTRICTED only accessable in CEN/MPI net or via CliSAP login  What does that mean?

View data via LAS: AQUA | TERRA

Access data via OPeNDAP: AQUA | TERRA

Data access via file system:
/data/icdc/atmosphere/modis_aqua_watervapor_pwc_temperature
/data/icdc/atmosphere/modis_terra_watervapor_pwc_temperature

 

Description

MODIS stands for MODerate resolution Imaging Spectroradiometer. This sensor, equipped with over 30 spectral channels from the visible into the infrared frequency range operates from aboard the EOS-TERRA and EOS-AQUA satellites since 2000 and 2002, respectively. Thanks to its high spectral resolution and the large number of different channels a large number of different atmospheric parameters can be retrieved. Here we refer to the columnar water vapor content and precipitable water content (PWC) data sets.

Similar to the data sets of the MODIS temperature profile data set the water vapor content and PWC data sets are derived by means of a statistical regression analysis. Vertical profiles of temperature, moisture and ozone measured globally by radiosondes are used to compute MODIS infrared band radiances using a radiative transfer / transmission model. A regression analysis between the computed radiances and the measured atmospheric profiles is carried out to derive the regression coefficients. These are subsequently applied to the actual MODIS radiance measurements to retrieve the profiles of atmospheric parameters - here the humidity which is subsequently vertically integrated to obtain estimates of the columnar water vapor content and PWC.

In addition, one can exploit that the degree with which near infrared (NIR) solar radiation reflected at the Earth's surface is absorbed in the atmosphere is a function of the atmospheric water vapor content. Therefore, radiances measured by the 5 MODIS NIR bands centered around the water vapor absorption line at 0.94 µm are used to derive the NIR columnar water vapor content with a look-up table procedure. Elements of the look-up table were pre-calculated using a radiative transfer / transmittance model and a spectroscopic data base.

More information about the data sets can be found on the MODIS-Atmosphere Group webpage and in the references section - here in particular in the article by King et al. (2003).

This is part of the level-3 MOD08/MYD08 data set derived from level-2 MOD05/MYD05 data of the MODIS Collection 6.1 product family, downloaded August 2018.

Last update of data set at ICDC: March 15, 2019

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Parameters

Name Unit Comments
Near Infrared (NIR) from MOD05_L2    
Mean water vapor content (clearsky) cm c
Mean water vapor content standard deviation (clearsky) | cm |
Mean water vapor content quality (clearsky)| -- | Number of: Questionable, Good, Very Good, Total Level-2 input pixel
Mean water vapor content (cloudy) | cm |
Mean water vapor content standard deviation (cloudy) | cm |
Mean water vapor content quality (cloudy)| -- | Number of: Questionable, Good, Very Good, Total Level-2 input pixel
Thermal Infrared from MOD07_2, total column
Mean PWC | cm |
Mean PWC standard deviation |cm |
Mean confidence flag weighted PWC | cm |
Mean confidence flag weighted PWC standard deviation | cm |
Mean confidence flag weighted PWC quality | -- | Number of: Questionable, Good, Very Good, Total Level-2 input pixel
Thermal Infrared from MOD07_2, surface to 680 hPa
Mean PWC680 | cm |
Mean PWC680 standard deviation |cm |
Mean confidence flag weighted PWC680 | cm |
Mean confidence flag weighted PWC680 standard deviation | cm |
Thermal Infrared from MOD07_2, 440 hPa to 10 hPa
Mean PWC10 | cm |
Mean PWC10 standard deviation |cm |
Mean confidence flag weighted PWC10 | cm |
Mean confidence flag weighted PWC10 standard deviation | cm |
||This is part of a composite data set
||(see MODIS Temperature profiles)

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Coverage, spatial and temporal resolution

Period and temporal resolution: 

  • 2000-02-24 to 2019-02-28 (MODIS EOS-TERRA)
  • 2002-07-04 to 2019-02-28 (MODIS EOS-AQUA)
  • Daily

Coverage and spatial resolution:

  • Global
  • Spatial resolution: 1° x 1°, cartesian grid
  • Geographic longitude: 180°W to 180°E
  • Geographic latitude: 90°S to 90°N
  • Dimension: 360 columns x 180 rows
  • Altitude: following terrain

Format:

  • NetCDF

Missing days:

  • TERRA: August 7-18 2000; June 16 - July 2 2001; March 20-27 & April 15 2002; December 21-22 2008
  • AQUA: July 30 - August 6 2002

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Data quality

The offered water vapor content data contain as a measure of uncertainty on the one hand the standard deviation of all level-2 grid cells used for the computation of the Level-3 product.

On the other hand, for some of the products so-called "quality assessed" level-3 data sets are offered. These are the result of a weighted averaging of the level-2 data where the confidence flags of the level-2 products are used as weights (in some modified way).

The distribution of these confidence intervals (from the level-2 data) is illustrated in the level-3 data via quality flag maps which contain the global distribution of the numbers of questionable, good, very good, and total useful level-2 pixels per level-3 grid cell.

This data set is from Collection 6.1 of the MODIS product family. Hence a substantial number inconsistencies and potential retrieval problems, which have been identified in the past product families (4, 5), has been taken care of in this newest MODIS product family (6). The main improvement in this newest release 6.1 over release 6.0 is the mitigation of the impact of electronic cross-talk between adjacent atmospheric frequency bands.

We refer to the documents listed in the References.

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Contact

Steve Platnick
MODIS - Atmosphere Level-3 Product Group
NASA / GSFC
email: steve.platnick (at) nasa.gov

Bo-Cai Gao
MODIS - Water Vapor Retrieval Group
NASA / GSFC
email: gao (at) neptune.nrl.navy.mil

Stefan Kern
ICDC / CEN / University of Hamburg
email: stefan.kern (at) uni-hamburg.de

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References

Data citation

Please cite the data as follows:

Platnick, S., et al., 2017. MODIS Atmosphere L3 Daily Product. NASA MODIS Adaptive Processing System, Goddard Space Flight Center, USA: dx.doi.org/10.5067/MODIS/MOD08_D3.061, last access date: 5/3/2019

(if MODIS EOS-AQUA data are used accordingly: dx.doi.org/10.5067/MODIS/MYD08_D3.061)

and acknowledge the source of your data download as:

Original MODIS collection 6.1 water vapor data provided in hdf format by https://ladsweb.modaps.eosdis.nasa.gov/ were downloaded in netCDF file format from the Integrated Climate Data Centre (ICDC), CliSAP, University of Hamburg, Hamburg, Germany, http://icdc.cen.uni-hamburg.de

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