# AlTiS Software for generating Time-Series of Water Levels from Radar Altimetry Data

Fabien Blarel, Damien Allain, Florence Birol, Sakaros Bogning, Robin Chevrier, Lucrèce Djeumeni, Wassim Fkaier, Frédéric Frappart, Yvan Gouzenes, Fabien Léger, et al.

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► To cite this version:

Fabien Blarel, Damien Allain, Florence Birol, Sakaros Bogning, Robin Chevrier, et al. AlTiS Software for generating Time-Series of Water Levels from Radar Altimetry Data. 2022 Ocean Surface Topography Science Team Meeting, Oct 2022, Venise, Italy. 10.24400/527896/a03-2022.3453. hal-04180138

HAL Id: hal-04180138

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Submitted on 11 Aug 2023

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# AITiS Software for generating Time-Series of Water Levels from Radar Altimetry Data

Fabien Blarel; Damien Allain; Florence Birol; Sakaros Bogning; Robin Chevrier; Lucrèce Djeumeni; Wassim Fkaier; Frédéric Frappart; Yvan Gouzenes; Fabien Léger; Rosemary Morrow; Fernando Niño

LEGOS, Université de Toulouse, CNES, CNRS, IRD, UPS

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AITiS (Altimetry Time Series) is a radar altimetry data processing and visualization software, tailored for fine-grained analysis of small scale water bodies.

Its goal is the obtaining **water-level time-series** derived from the altimetry measurements, but it can also be used to generate time series of any altimetry-based parameters (e.g., corrections applied to the range, backscattering coefficients, or brightness temperatures).

Since September 2020, AlTiS replaces MAPS (Multi-mission Altimetry Processing Software) [Frappart et al. Marine Geodesy, 2015]. AlTiS project is part of THEIA Water Volume scientific expertise center of the French Earth System Research Infrastructure "Data Terra".

## Graphical User Interface

Using a **Graphical User Interface (GUI)**, without requiring any particular skills in data processing, the user can handle altimetry data in order to :

* **Plot several parameters of altimetric measurement** like surface height, altimetric range, atmospheric corrections applied to the range (ionospheric correction and wet and dry tropospheric corrections) as a function of latitude/longitude.

* **Display along-track characteristic parameters of the waveform** like the backscatter coefficient, and peakiness.

* **Using a (Landsat) background map**, easily select altimetric measurements to remove outliers.

* **Generate water height time series** from the valid altimetry data previously selected

<figure><img src="image_6.png" /><figcaption>Screenshot of AlTiS GUI : 4 displays windows in order to edit altimeter measurement graphically</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>On left-hand side, mean time series computed and its variability associated; on right-hand side, the distributions.</figcaption></figure>

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[Normandin et al., Remote Sensing, 2018]

An example of the altimetry data editing in the case of a river in the Inner Niger Delta area :

* First, a rough selection of the altimetry data is performed: (a) all altimetry data located a few kilometers away from the center of the river are selected (left panel), the major topographic features, such hills, river banks, tributaries, etc. can be identified (central panel), temporal variations of the altimetry signal cannot be related to any hydrological signal (right panel).

* Then, a more accurate selection is made; (b) the number of data is decreasing and outliers are removed (left panel), the shape of the river and its temporal variations in width (central panel) and height (left panel) becomes clearer.

* This process is repeated until the final selection is achieved; (c)

A regularly updated documentation is available on the AlTiS wiki.

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## AITiS users

Today, more than **70 users** of over **21 countries** have processed altimetric data to generate water level time series with AlTiS software. It is used for research and training activities.

The CTOH holds its own **AlTiS teaching courses for students, engineers and researchers** in the Midi-Pyrénées Observatory in Toulouse, France. In addition, it has created an **AlTiS user network** to provide information about software updates and new altimetric products.

On the current year, the CTOH has already answered more than 220 data requests.

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**HydroWeb** uses AlTiS for its research and validation studies.

## CTOH Altimetric products available for AlTiS processing

<table><thead><tr><th rowspan="2">Mission</th><th rowspan="2">Prod. Name</th><th colspan="2">Cycle</th><th colspan="2">Date</th><th rowspan="2">Orbit</th></tr><tr><th>start</th><th>end</th><th>start</th><th>end</th></tr></thead><tbody><tr><td rowspan="2">Cryosat-2</td><td>cs2_b_gop_c_gdr</td><td>1</td><td>11</td><td>2010-07-16</td><td>2021-02-25</td><td>Nominal orbit (369 days)</td></tr><tr><td>cs2_b_ice_d_gdr</td><td>2</td><td>10</td><td>2010-07-16</td><td>2021-02-25</td><td>Nominal orbit (369 days)</td></tr><tr><td rowspan="2">EnvSat</td><td>env_a_esa_v0300_sgdr</td><td>6</td><td>94</td><td>2002-05-14</td><td>2010-10-23</td><td>Nominal orbit (35 days)</td></tr><tr><td>env_b_esa_v0300_sgdr *</td><td>95</td><td>113</td><td>2010-10-26</td><td>2012-04-08</td><td>Drifting orbit</td></tr><tr><td>ERS-2</td><td>ers2_a_ctoh_v0100_gdr</td><td>1</td><td>89</td><td>1995-05-17</td><td>2003-11-24</td><td>Nominal orbit (35 days)</td></tr><tr><td rowspan="3">Jason-1</td><td>ja1_a_cnes_e_sgdr</td><td>1</td><td>259</td><td>2002-01-15</td><td>2009-01-26</td><td>Nominal orbit (10 days)</td></tr><tr><td>ja1_b_cnes_e_sgdr</td><td>262</td><td>374</td><td>2009-02-10</td><td>2012-03-03</td><td>Interleaved orbit (10 days)</td></tr><tr><td>ja1_c_cnes_e_sgdr *</td><td>500</td><td>537</td><td>2012-05-07</td><td>2013-06-21</td><td>Drifting orbit</td></tr><tr><td rowspan="4">Jason-2</td><td>ja2_a_cnes_d_sgdr</td><td>0</td><td>303</td><td>2008-07-04</td><td>2016-10-02</td><td>Nominal orbit (10 days)</td></tr><tr><td>ja2_b_cnes_d_sgdr</td><td>305</td><td>327</td><td>2016-10-13</td><td>2017-05-17</td><td>Interleaved orbit (10 days)</td></tr><tr><td>ja2_c_cnes_d_sgdr</td><td>500</td><td>537</td><td>2017-07-11</td><td>2018-07-18</td><td>Long-repeat-orbit (LRO)</td></tr><tr><td>ja2_d_cnes_d_sgdr *</td><td>600</td><td>644</td><td>2018-07-25</td><td>2019-10-01</td><td>Geodetic orbit</td></tr><tr><td rowspan="2">Jason-3</td><td>ja3_a_cnes_f_sgdr</td><td>0</td><td>227</td><td>2016-02-12</td><td>2022-04-07</td><td>Nominal orbit (10 days)</td></tr><tr><td>ja3_b_cnes_f_sgdr</td><td>300</td><td>312</td><td>2022-04-25</td><td>2022-07-27</td><td>Interleaved orbit (10 days)</td></tr><tr><td rowspan="2">Sentinel-3A</td><td>s3a_a_lrm_f06_gdr</td><td>1</td><td>89</td><td>2016-03-01</td><td>2022-08-30</td><td>Nominal orbit (27 days)</td></tr><tr><td>s3a_a_wat_%_sgdr</td><td>1</td><td>89</td><td>2016-03-01</td><td>2022-08-30</td><td>Nominal orbit (27 days)</td></tr><tr><td rowspan="4">Sentinel-3B</td><td>s3b_a_lrm_f06_gdr</td><td>3</td><td>19</td><td>2018-05-11</td><td>2018-11-27</td><td>S3A Tandem orbit (27 days)</td></tr><tr><td>s3b_a_wat_%_sgdr</td><td>2</td><td>19</td><td>2018-05-11</td><td>2018-11-27</td><td>S3A Tandem orbit (27 days)</td></tr><tr><td>s3b_b_lrm_f06_gdr</td><td>19</td><td>70</td><td>2018-11-28</td><td>2022-09-01</td><td>Nominal orbit (27 days)</td></tr><tr><td>s3b_b_wat_%_sgdr</td><td>19</td><td>70</td><td>2018-11-28</td><td>2022-09-01</td><td>Nominal orbit (27 days)</td></tr><tr><td rowspan="2">Sentinel-6A</td><td>s6a_a_lrm_f06_gdr</td><td>4</td><td>65</td><td>2020-12-17</td><td>2022-08-15</td><td>Nominal orbit (10 days)</td></tr><tr><td>s6a_a_sar_f06_gdr</td><td>4</td><td>65</td><td>2020-12-17</td><td>2022-08-15</td><td>Nominal orbit (10 days)</td></tr><tr><td rowspan="2">Saral</td><td>srl_a_cnes_f_sgdr</td><td>1</td><td>35</td><td>2013-03-14</td><td>2016-07-04</td><td>Nominal orbit (35 days)</td></tr><tr><td>srl_b_cnes_f_sgdr *</td><td>100</td><td>162</td><td>2016-07-04</td><td>2022-07-18</td><td>Drifting orbit</td></tr><tr><td>Topex</td><td>tpx_a_cash_v0220_gdr</td><td>10</td><td>359</td><td>1992-12-21</td><td>2002-06-22</td><td>Nominal orbit (10 days)</td></tr></tbody></table>

* Product supplied to expert user only.

AlTiS accepts **CTOH GDR altimetry products** (Level 2 high frequency 10/20/40Hz data supplied by the CTOH). These data have been specifically conditioned to optimize the data size by making a geographical selection and includes the right altimetry parameters for hydrological studies.

### Data requests

AlTiS can process several altimetric data products from the missions : Jason-1/2/3, ERS-2, ENVISAT, SARAL, Sentinel-3A/B, and soon, Sentinel-6/Jason-CS and the nadir altimeter onboard SWOT. They are supplied for free through a web request [form on the CTOH website](#).

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## Hydrological applications

AlTiS is mainly employed for **hydrological applications** and can be used for **training courses on radar altimetry** at bachelor or master levels. It is also a very **convenient tool to analyse** the radar altimetry data contained in the GDR over any type of land surfaces.

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An example of a time series of water level at **Lambaréné (Ogooué River Basin in Gabon in Equatorial Africa)** from the in-situ gauge record (black continuous line), the **multi-mission altimetry-based** record (ERS-2 data are represented with diamonds, ENVISAT with blue crosses on its nominal orbit and with green triangles on its second orbit, Cryosat-2 with green-blue stars, SARAL with red circles, Sentinel-3 with purple dots) [Bogning, Sakaros, et al., Remote Sensing, 2018].

## Open source software

AlTiS is free software developed by **CTOH** as part of its activities as a National Observation Service. AlTiS is released as open source under the CeCill License and target GNU/Linux and, Windows 10 operating systems under python3 environment. [AlTiS is available on GitLab.](https://gitlab.cns.fr/aitis)

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