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Content: General | Altimeter Data | Processing Strategy | Data Holding | Data Versions | Data Formats | Citation

General

Satellite altimetry has the potential to measure water levels of lakes, reservoirs, rivers and wetlands from space. However, satellite altimetry is limited due to its measuring technique, since it can only measure in nadir direction which means that the inland water body has to be crossed. The accuracy of the water level time series vary between few centimeters for large lakes and few decimeters for small rivers. The temporal resolution of the water level time series depends on the used altimeter satellites (e.g. 10 days for Jason-3, 35 days for Envisat) and the number of tracks crossing the inland water body. The combination of different altimeter missions can increase the temporal resolution. The figure (left) shows the water level time series of Ray Roberts located in the United Stats which is based on Jason-2/-3 (blue) and Jason-3 real-time data (red). Real-time data allows us to create water level time series with a delay of 1-2 days after the altimeter satellite crossed the inland water body.

Example of Water Level Time Series from Satellite Altimetry
Altimeter Satellites

For the estimation of water heights, multi-mission altimeter data are used. The following figure gives an overview of the past, current and future altimeter missions since 1985.


Processing Strategy

The processing strategy of DAHITI which is described in detail in Schwatke et al. (2015) is based on an extended outlier detection and a Kalman filtering.

Data Holding

DAHITI as a global database currently provides 11051 water level time series distributed over all continents, except Antarctica. In Africa (2164 time series), Asia (2013), Australia (54), Europe (1029), North America (1521), and South America (4090) water level time series are available. The water level time series in DAHITI are freely available and can be downloaded after a short registration process. The amount of water level time series is permanently increasing.

Data Versions

--- Version v6.0 ---

This version uses the standard DAHITI approach described in Schwatke et al. (2015).
In this version, the following models and geophysical corrections are applied.

Correction Source/Model Reference
Wet Troposphere Vienna Mapping Functions 3 (VMF3) Landskron and Böhm, 2018
Dry Troposphere Vienna Mapping Functions 3 (VMF3) Landskron and Böhm, 2018
Ionosphere NOAA Ionosphere Climatology 2009 (NIC09) Scharro and Smith, 2010
Solid Earth Tide IERS Convention 2010 Petit and Luzum, 2010
Pole tide IERS Convention 2010 Petit and Luzum, 2010
Range bias MMXO-16 Bosch et al., 2014
Geoid EIGEN-6C4 Förste et al., 2014

Data Format

Water level time series can be download in ASCII, NetCDF, CSV and JSON format.

--- ASCII ---

# DAHITI-ID       : 10146
# Target name     : Ray Roberts, Reservoir
# Continent       : North America
# Country         : United States of America
# Longitude       : -97.0557
# Latitude        : 33.3615
# Points          : 355
# Software        : 6.0
# Download        : 2020-03-09 07:44:26 (UTC)
# Dataset         : water-level-altimetry
# ----------------------------------------
# column 1        : date [yyyy-mm-dd]
# column 2        : water level from altimetry [m]
# column 3        : error [m]
# ----------------------------------------
2008-07-23 192.395 0.005
2008-08-12 192.345 0.028
2008-09-01 192.481 0.021
2008-09-11 192.903 0.064
2008-10-21 192.288 0.056
...
2020-01-27 193.427 0.115
2020-02-16 192.970 0.006
2020-02-25 192.758 0.003

--- NetCDF ---

user@dahiti:/> ncdump -h 10146_water_level_altimetry.nc
netcdf \10146_water_level_altimetry {
dimensions:
        time = 355 ;
variables:
        string date(time) ;
                date:standard_name = "UTC Date (YYYY-MM-DD)" ;
        float water_level(time) ;
                water_level:standard_name = "Water Levels derived from Satellite Altimetry;
                water_level:source = "Satellite Altimetry;
                water_level:unit = "m" ;
        float error(time) ;
                error:standard_name = "Error of Water Levels" ;
                error:unit = "m" ;
// global attributes:
                :dahiti_id = "10146" ;
                :dataset = "water-level-altimetry" ;
                :target_name = "Ray Roberts, Reservoir" ;
                :location = "None" ;
                :continent = "North America" ;
                :country = "United States of America" ;
                :longitute = "-97.0557" ;
                :latitude = "33.3615" ;
                :software = "6.0" ;
                :institution = "DGFI-TUM" ;
                :source = "DAHITI" ;
                :url = "https://dahiti.dgfi.tum.de/10146/" ;
                :creation_date = "2020-03-09 07:53:09" ;
}

--- CSV ---

date,water level,error
2008-07-23,192.395,0.005
2008-08-12,192.345,0.028
2008-09-01,192.481,0.021
...
2020-01-27,193.427,0.115
2020-02-16,192.970,0.006
2020-02-25,192.758,0.003

--- JSON ---

{
"info": {
    "dahiti_id": "10146",
    "target_name": "Ray Roberts, Reservoir",
    "location": "None",
    "latitude": "33.3615",
    "continent": "North America",
    "country": "United States of America"
    "longitute": "-97.0557", 
    "software": "6.0",
    "source": "DAHITI",
    "institution": "DGFI-TUM", 
    "url": "https://dahiti.dgfi.tum.de/10146/",
    "dataset": "water-level-altimetry", 
    "creation_date": "2020-03-09 07:46:36",
    }, 
"data": [
    {"error": 0.005, "water_level": 192.394564051, "date": "2008-07-23"},
    {"error": 0.0278, "water_level": 192.345119619, "date": "2008-08-12"},
    {"error": 0.0213, "water_level": 192.481309165, "date": "2008-09-01"},
    ...
    {"error": 0.0058, "water_level": 192.969924123, "date": "2020-02-16"},
    {"error": 0.0033, "water_level": 192.757562858, "date": "2020-02-25"}
    ]
}

Citation