OSMOSE Database Manual Microwave T3-D06 (TN
#03)

Simon Boitard, Arnaud Mialon, Nemesio Rodríguez-Fernández

► To cite this version:

Simon Boitard, Arnaud Mialon, Nemesio Rodríguez-Fernández. OSMOSE Database Manual Mi-crowave T3-D06 (TN #03). SO-TN-CB-GS-0115, CESBIO. 2023, pp.SO-TN-CB-GS-0115. hal-04840251

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<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
OSMOSE
Database Manual Microwave
T3-D06 (TN #03)

Version : 1.0 (22 Sept. 2023)

Ref.: SO-TN-CB-GS-0115
OSMOSE
Database Manual Microwave
T3-D06 (TN #03)

CESBIO-SMOS report SO-TN-CB-GS-0115

Simon Boitard¹, Arnaud Mialon¹, Nemesio J. Rodríguez-Fernández¹, ??? ¹

¹ CESBIO

Université de Toulouse, CNES/CNRS/INRAE/IRD/UT3, 18, Avenue Edouard Belin, 31401 Toulouse, France

<table><thead><tr><td>Release</td><td>Date</td><td>Details</td><td>Editors</td></tr></thead><tbody><tr><td>1</td><td>22 Sept 2023</td><td>First version</td><td>Arnaud Mialon</td></tr></tbody></table>

Contact Arnaud Mialon arnaud.mialon@univ-tlse3.fr
# Contents

<table><tr><td>List of Figures</td><td>4</td></tr><tr><td>List of Tables</td><td>4</td></tr><tr><td>1 Acronyms</td><td>5</td></tr><tr><td>2 Introduction</td><td>6</td></tr><tr><td>2.1 Purpose of the document</td><td>6</td></tr><tr><td>3 Input Data and their content</td><td>7</td></tr><tr><td>3.1 General Considerations</td><td>7</td></tr><tr><td>3.2 SMOS</td><td>7</td></tr><tr><td>3.3 AMSRE</td><td>11</td></tr><tr><td>3.4 AMSR2</td><td>16</td></tr><tr><td>3.5 ERA 5</td><td>17</td></tr><tr><td>4 VOD Output Data file</td><td>19</td></tr><tr><td>4.1 Naming convention</td><td>19</td></tr><tr><td>4.2 file content</td><td>20</td></tr><tr><td>References</td><td>21</td></tr><tr><td>Bibliography</td><td>21</td></tr></table>
List of Figures

<table><tr><td>1</td><td>Examples of daily Brightness temperatures (in K.) from the AMSRE sensor, Vertical polarisation. Top figure is the cylindric 0630 product from the MEaSURES; Bottom figure is the combined cylindric and north pole 0630 products. Note that the two examples are not for the same day.</td><td>12</td></tr><tr><td>2</td><td>Erroneous acquisition time in the original MEaSURES file</td><td>13</td></tr><tr><td>3</td><td>Acquisition time in the OSMOSE AMSRE products from (6)</td><td>14</td></tr><tr><td>4</td><td>Examples of the time of a daily ERA5 product done for the OSMOSE project.</td><td>17</td></tr></table>

List of Tables

<table><tr><td>1</td><td>Applicable documents</td><td>6</td></tr><tr><td>2</td><td>Applicable documents</td><td>6</td></tr><tr><td>3</td><td>Content of the L3 Brightness Temperatures Product</td><td>10</td></tr><tr><td>4</td><td>File content of the AMSRE Brightness Temperatures Product</td><td>15</td></tr><tr><td>5</td><td>File content of the AMSR2 Brightness Temperatures Product</td><td>16</td></tr><tr><td>6</td><td>ERA5 file content</td><td>18</td></tr><tr><td>7</td><td>VOD file content</td><td>20</td></tr><tr><td>8</td><td>Bit signification of the Scene_Flags</td><td>21</td></tr></table>
# 1 Acronyms

<table><tr><td>2S</td><td>Two Stream Radiative Transfer Model</td></tr><tr><td>AMSRE</td><td>Advanced Microwave Scanning Radiometer-EOS</td></tr><tr><td>AMSR2</td><td>Advanced Microwave Scanning Radiometer 2</td></tr><tr><td>ADF</td><td>Auxiliary Data File</td></tr><tr><td>ATBD</td><td>Algorithm Theoretical Baseline Document</td></tr><tr><td>CATDS</td><td>Centre Aval de Traitement des Données SMOS</td></tr><tr><td>CESBIO</td><td>Centre d'Etudes Spatiales de la Biosphère</td></tr><tr><td>DQX</td><td>Data Quality Index</td></tr><tr><td>EASE</td><td>Equal-Area Scalable Earth Grid</td></tr><tr><td>ECMWF</td><td>European Centre for Medium-range Weather Forecasting</td></tr><tr><td>GCOM</td><td>Global Change Observation Mission</td></tr><tr><td>JAXA</td><td>Japan Aerospace Exploration Agency</td></tr><tr><td>L-MEB</td><td>L - band Microwave Emission of the Biosphere</td></tr><tr><td>LSB / MSB</td><td>Lowest / Most Significant Bit *</td></tr><tr><td>MD</td><td>Cardioid Model</td></tr><tr><td>RFI</td><td>Radiometric Frequency Interference</td></tr><tr><td>RTM</td><td>Radiative Transfer Model</td></tr><tr><td>SM</td><td>Soil Moisture</td></tr><tr><td>SMOS</td><td>Soil Moisture and Ocean Salinity</td></tr><tr><td>Tau</td><td>Vegetation Optical thickness</td></tr><tr><td>TB</td><td>Brightness Temperature</td></tr><tr><td>VOD</td><td>Vegetation Optical Depth</td></tr></table>
# 2 Introduction

## 2.1 Purpose of the document

The purpose of this document is to present the microwave dataset of the VOD chains, both input data and output products. It describes the dataset used to derive the VOD at different frequencies, i.e. L band from the SMOS satellite mission, the C and X bands from the AMSR-E/2 satellite missions. It also provides details about the name of the files as well as their contents.

### 2.1.1 Related documents

<table><caption>Table 1: Applicable documents</caption><thead><tr><td>Id.</td><td>Ref.</td><td>Description</td></tr></thead><tbody><tr><td>AD. 1</td><td>ESA-EOPSM-SMOS-SOW-3918</td><td>Statement of Work for the project "10 YEARS OF SMOS - PASSIVE MICROWAVE VEGETATION OPACITY STUDY (PM-VO-S).</td></tr></tbody></table>

### 2.1.2 Reference documents

<table><caption>Table 2: Applicable documents</caption><thead><tr><td>Id.</td><td>Ref.</td><td>Description</td></tr></thead><tbody><tr><td>RD. 2</td><td>SO-TN-CB-CA-0001</td><td>CATDS Level 3 Data Product Description<br>Soil Moisture and Brightness Temperature</td></tr></tbody></table>
# 3 Input Data and their content

## 3.1 General Considerations

All the products discussed in the following are provided for the OSMOSE project as:

* **Format**: netcdf files, characterized by the .nc extension name

* **Grid system**: EASE Grid version 2 ((1), (2)), that is 25km x 25km at 30deg of latitude

* **Grid dimensions**: global earth is covered by a matrix of 584x1388 pixels

If the initial datasets are provided at different spatial and temporal resolutions than the final one, details are reported in the sections corresponding to each dataset.

## 3.2 SMOS

The SMOS data used for this project are delivered by the CATDS (Centre Aval de Traitement des Données SMOS) located in Brest (France). All data are freely available from the website https://www.catds.fr/ and through the ftp:

* **ftp address**: ftp.ifremer.fr

* **ftp user**: ext-catds-cpdc

* **ftp password**: catds2010

All the SMOS data are delivered in the format presented in the previous section 3.1.

### 3.2.1 Level 3 Brightness Temperatures, TB

The Level 3 Brightness Temperature product is a daily global polarised brightness temperature product, arranged by incidence angle values, in full polarisations (H, V, stokes3, and stockes4). It includes all brightness temperatures acquired that day, transformed to ground polarisation reference frame (H and V polarisation), binned (5°), and averaged into fixed angle classes. Bin 9 corresponds to SMAP incidence angle (40° +/- 2°), and bin 15 is a placeholder for the time being. Ascending and descending orbits are processed separately.

#### Naming Convention

Filenames are SM_OPER_MIR_CDF3Tx_yyyymmddThhmmss_YYYYMMDDTHHMMSS_vvvCCC_n with

* **SM**: in this specific case, it stands for the SMOS mission

* **OPER/REPR**: file class, indicates whether the data is produced in a nominal OPER or reprocessing REPR

* **MIR**: MIRAS, as the name of the instrument

* **CDF3Tx**

- **C** = CATDS

- **D** = for daily nominal product
- F = for full polarisation

- 3T = Level 3 Brightness Temperature Products

- x = "A" for ascending orbit and "D" for descending orbit

* yyymmddThhmmss: sensing start time for the data contained in the product

* With yyyy year

* mm month

* dd day of the month

* hh hour

* mm minutes

* ss seconds

* vvv: version number of the processor generating the product

* ccc: file counter, used to make a distinction among products having all other filename identifiers identical: the higher the file counter, the more recent the product

* n: processing site (C-PDC=7, C-EC SM=8, C-EC OS=9)

organised as follows on the CATDS ftp:

SM/GRIDDED/L3/OPER/product type/year/day of the year, where product type can be MIR_CDF3TA or MIR_CDF3TD depending on orbits type, and day of the year is between 001 (1st January) and 365/366 (31st December).

## Product content

<table><thead><tr><td>Variable Name</td><td>Description</td></tr></thead><tbody><tr><td>lat and lon</td><td>Geographic coordinates: Vectors of latitudes and longitudes (in degree) of the grid point. The dimensions of "lat" and "lon" are 584x1 and 1388x1 respectively, corresponding to the 584x1388 nodes of the EASE version 2, 25km cylindrical grid.</td></tr><tr><td>inc and dinc</td><td>Centre (inc) and width (dinc) of each class of angle in degree Their dimensions are 15x1</td></tr></tbody></table>

The 2 following parameters are presented as a 584x1388 matrix

<table><tr><td>X_Swath</td><td>Abscissa of the dwell line (in km): The sign of the value is relative to the direction of the satellite. It is positive if it is to the right and negative if it is to the left of the satellite subtrack</td></tr><tr><td>Grid_Point_Mask</td><td>Flag indicating land/sea USGS content, coastline</td></tr></table>
distance, and Ice content.
See at the end of the document for a complete
description of this flag

All the following parameters have 3 dimensions: 15x584x1388

<table><tr><td>BT_H, BT_V<br>BT_3, BT_4</td><td>Averaged brightness temperature (in Kelvin) by<br>angle class in H-pol, V-pol, 3rd Stokes parameter<br>and 4th Stokes parameter respectively, over current<br>Earth fixed grid point, obtained by rotating the L1c<br>data</td></tr><tr><td>Pixel_Radiometric_Accuracy_H<br>Pixel_Radiometric_Accuracy_V<br>Pixel_Radiometric_Accuracy_3<br>Pixel_Radiometric_Accuracy_4</td><td>Error accuracy measurement (in Kelvin) associated<br>to the averaged brightness temperature by class of<br>angle presented in the previous field, extracted in<br>the direction of the pixel.</td></tr><tr><td>Pixel_BT_Standard_Deviation_H<br>Pixel_BT_Standard_Deviation_V<br>Pixel_BT_Standard_Deviation_3<br>Pixel_BT_Standard_Deviation_4</td><td>Brightness temperature standard deviation (in<br>Kelvin) by class of angle.</td></tr><tr><td>Incidence_Angle</td><td>Incidence angle value (in degree) by class of angle<br>corresponding to the measured BT values over<br>current Earth fixed grid point</td></tr><tr><td>Azimuth_Angle</td><td>Azimuth angle value (in degree) by class of angle<br>corresponding to the measured brightness<br>temperature value over current Earth fixed grid<br>point</td></tr><tr><td>Footprint_Axis1<br>Footprint_Axis2</td><td>Elliptical averaged footprint major (and minor<br>respectively) semi-axis value by class of angle.<br>Averaged direction cosine for Xi and Eta,<br>respectively, by angle class</td></tr><tr><td>Xi and Eta</td><td>Xi and Eta referred to the antenna frame</td></tr><tr><td>Nviews</td><td>Number of brightness temperature views used to<br>compute angle class averages.</td></tr><tr><td>Days<br>UTC_Seconds<br>UTC_Microseconds</td><td>Measurement acquisition time in UTC at which<br>the averaged brightness temperature was taken<br>Day count begins on the 1st of January 2000<br>seconds and microseconds are relative to the current day in UTC</td></tr><tr><td>Nb_RFI_Flags</td><td>Number of views flagged as<br>potentially contaminated by RFI</td></tr></table>
<table><caption>Table 3: Content of the L3 Brightness Temperatures Product</caption><tr><td>Nb_SUN_Flags</td><td>Number of views flagged as contaminated by the sun</td></tr></table>
## 3.3 AMSRE

### 3.3.1 Main information

The Advanced Microwave Scanning Radiometer for EOS (AMSR-E) aboard NASA's Aqua satellite, provides Brightness Temperatures at Vertical and Horizontal polarisations at an incidence angle of 55 deg, for the 6 fre- quencies 89.0 GHz, 36.5 GHz, 23.8 GHz, 18.7 GHz, 10.65 GHz and 6.925 GHz. The OSMOSE project focuses on the C and X bands, so only the 6.925 GHz and 10.65 GHz are kept.

* Radiometric accuracy: <0.5 K (7) et spécifiquement 0.3 K. en bande C, et 0.6 K. en bande X

* Spatial Resolution: 51 x 29 km (10.65 GHz, X-band), 75 x 43 km (6.925 GHz, C-band)

* Incidence Angle: 55 deg.

The purpose of the OSMOSE project is to set up a homogenized VOD data set, on the EASE Grid version 2 (25 km). The NSIDC provides the AMSRE data on such grid, called the "MEaSURES dataset", but the data are split into two products, one on the global projection, but only covering latitudes lower than 70 deg. (see top Figure 1) and one on the polar grid. The two projections are then combined daily (ascending/descending orbits processed separately) to ensure a global coverage, i.e. including the high latitudes (see example bottom Figure 1). The MEaSURES database encompasses different passive microwave sensors (e.g. SSM/I, SSMR...), which are inter-calibrated and for which the projection on the EASE Grid 2 is properly done, in case the methods developed for the OSMOSE project can be applied to the other passive microwave satellites.

* Name of dataset: MEaSURES Calibrated Enhanced-Resolution Passive Microwave Daily EASE-Grid 2.0 Brightness Temperature ESDR, Version 1

* ID: NSIDC-0630

* DOI: 10.5067/MEASURES/CRYOSPHERE/NSIDC-0630.001

* Website: https://nsidc.org/data/nsidc-0630/versions/1

* Reference: (5), (3)

* Temporal coverage: 01 June 2002 04 October 2011

### 3.3.2 Time

In the MEaSURES dataset, the time of acquisition of the TB is incorrect and set to a constant value for all orbits in the daily files (see Fig. 2).

To process the AMSRE TB for the C and X bands and produce relevant VOD, meteorological information at the time of the data acquisition is needed (skin temperature, air temperature at 2m, etc). The acquisition time of the AMSRE TB from the MEaSURES dataset was corrected using the NSIDC-0301 dataset (6). In this dataset, the AMSRE TB are distributed as daily binary files on the 25km EASE Grid (584 latitude and 1388 longitude). These TB come with separate daily binary files holding the acquisition time of the TB in minutes since 00UTC. There is one-time file per orbit type (ascending or descending) making a total of two time files per day identified with the .TIM extension.

Once downloaded, the time files need to be uncompressed and slightly reprojected from the EASE 25km to the EASE 2 25km Grid. From there, the time in the decompressed reprojected .TIM files can be written out in the AMSRE products (see Fig. 3).
<figure><img src="image_2.png" /></figure>

Figure 1: Examples of daily Brightness temperatures (in K.) from the AMSRE sensor, Vertical polarisation. Top figure is the cylindric 0630 product from the MEaSURES; Bottom figure is the combined cylindric and north pole 0630 products. Note that the two examples are not for the same day.
<figure><img src="image_3.png" /><figcaption>Figure 2: Erroneous acquisition time in the original MEaSURES file</figcaption></figure>
<figure><img src="image_4.png" /><figcaption>Figure 3: Acquisition time in the OSMOSE AMSRE products from (6)</figcaption></figure>
### 3.3.3 Naming convention

For the OSMOSE project, one file is created per frequency and per orbit, with name as: `OSMOSE_TB_AMSRE_f_O_YYYYMMDD_001.nc`

* OSMOSE: specifies that the format is the one defined for the OSMOSE project

* TB: Brightness Temperatures

* f: 1 letter that specifies the frequency, C or X

* O: 1 letter that specifies the orbit, either A for Ascending or D for Descending

* YYYY: 4-digit number that stands for the year

* MM: 2-digit number that stands for the month

* DD: 2-digit number that stands for the day

For instance, `"OSMOSE_TB_AMSRE_C_D_20110927_001.nc"` corresponds to AMSRE TB at C band, for the Descending orbit, in the OSMOSE format (section 3.1), for September 27, 2011.

### 3.3.4 File Content

<table><caption>Table 4: File content of the AMSRE Brightness Temperatures Product</caption><tr><td>days</td><td>days since 1972-01-01 00:00:00, written as a double, dim=1</td></tr><tr><td>x</td><td>coordinates before reprojection, in meters, written as double, vector dim=1x1388 values between -1.736753E7 and 1.736753E7</td></tr><tr><td>y</td><td>coordinates before reprojection, in meters, written as double, vector dim=1x584 values between -7294863.289, 7294863.289</td></tr><tr><td>lon</td><td>longitude in degrees, written as double, vector dim=1x1388</td></tr><tr><td>lat</td><td>latitude in degrees, written as double, vector dim=1x584</td></tr><tr><td>BT_V</td><td>Brightness Temperatures in Kelvin, Vertical polarisation, written as float, 2D matrix dim=1388x584</td></tr><tr><td>BT_H</td><td>Brightness Temperatures in Kelvin, Horizontal polarisation, written as float, 2D matrix dim=1388x584</td></tr><tr><td>Incidence_Angle</td><td>Incidence Angle in degrees, written as float, 2D matrix dim=1388x584</td></tr><tr><td>Minutes</td><td>minutes since 2011-01-01 00:00:00, written as float, 2D matrix dim=1388x584</td></tr><tr><td>Pixel_BT_Standard_Deviation_V</td><td>Standard Deviation of Brightness Temperatures, vertical polarisation, written as float 2D matrix dim=1388x584</td></tr><tr><td>Pixel_BT_Standard_Deviation_H</td><td>Standard Deviation of Brightness Temperatures, horizontal polarisation, written as float 2D matrix dim=1388x584</td></tr></table>

`Pixel_BT_Standard_Deviation_V/H` are NOT an uncertainty nor a radiometric accuracy, but a standard deviation of the measurements used to derive TB, see (3)
## 3.4 AMSR2

The AMSR2 sensor is onboard the GCOM-W1 satellite, which was launched in July 2012 by the JAXA. It provides brightness temperatures at Vertical and Horizontal polarization, at an incidence angle of ~ 55° deg.. The data are split between Ascending/Descending orbits, which correspond to an overpassing time of 13:30/01:30.

* Name of dataset: LEVEL3

* original spatial resolution: 0.25 deg

* Website: https://suzaku.eorc.jaxa.jp/

* Reference: (8), (4)

* Temporal coverage:

### 3.4.1 Naming convention

For the OSMOSE project, one file is created per frequency and per orbit, with the following convention: **OSMOSE_TB_AMSR2_f_O_YYYYMMDD_001.nc**

* OSMOSE: specifies that the format is the one defined for the OSMOSE project

* TB: Brightness Temperatures

* f: 1 letter that specifies the frequency, C or X

* O: 1 letter that specifies the orbit, either A for Ascending or D for Descending

* YYYY: 4-digit number that stands for the year

* MM: 2-digit number that stands for the month

* DD: 2-digit number that stands for the day

For instance, "OSMOSE_TB_AMSR2_C_A_20110927_001.nc" corresponds to AMSR2 TB at C band, for the Ascending orbit, in the OSMOSE format (section 3.1), for September 27, 2011.

### 3.4.2 File Content

<table><caption>Table 5: File content of the AMSR2 Brightness Temperatures Product</caption><tr><td>days</td><td>days since 1972-01-01 00:00:00, written as a long, dim=1</td></tr><tr><td>lon</td><td>longitude in degrees, written as float, vector dim=1x1388</td></tr><tr><td>lat</td><td>latitude in degrees, written as float, vector dim=1x584</td></tr><tr><td>BT_V</td><td>Brightness Temperatures in Kelvin, Vertical polarisation, written as float, 2D matrix dim=1388x584</td></tr><tr><td>BT_H</td><td>Brightness Temperatures in Kelvin, Horizontal polarisation, written as float, 2D matrix dim=1388x584</td></tr><tr><td>Incidence_Angle</td><td>Incidence Angle in degrees, written as double, 2D matrix dim=1388x584</td></tr><tr><td>Minutes</td><td>minutes since the beginning of the day, written as float, 2D matrix dim=1388x584</td></tr></table>
<figure><img src="image_5.png" /><figcaption>Figure 4: Examples of the time of a daily ERA5 product done for the OSMOSE project.</figcaption></figure>

## 3.5 ERA 5

### 3.5.1 General Information

ERA 5 is the re-analysis of climate data from ECMWF, which provides various atmospheric and surface geo-physical information every hour, on a 0.25deg spatial resolution grid.

For the OSMOSE project, we used a subset of the catalog available from the website https://cds.climate.copernicus.eu/cdsapp#/dataset/reanalysis-era5-pressure-levels?tab=form, that is described in the next section.

The ERA5 are pre-processed for the applications to 1/ use only the closest time slot to the satellite over-passing time. It means for each satellite used in this project, and for each orbit, the hourly ERA5 data may change, as displayed in Figure 4 2/ spatially interpolated on the EASE-Grid version 2.

### 3.5.2 Naming convention

The ERA5 processed for the OSMOSE project are renamed as the following convention:

**OSMOSE ERA5 XXXX F O YYYYMMDD 001.nc**

with each item corresponding to

* OSMOSE: Optical SMOS Experiment, specifies that the ERA5 specifically processed for the OSMOSE project

* ERA5: ECMWF re-analysis data ERA version 5

* XXXX: instrument, can be either SMOS, AMSRE, or AMSR2.

* F: letter relative to the frequency band; can be either L, C or X

* O: stands for the orbit overpass, Ascending or Descending

* YYYY: 4-digit for year

* MM: 2-digit for month
* DD: 2-digit for day

* 001: number of times the product has been created

### 3.5.3 File Content

Each file contains the following fields that are needed to perform the retrieval.

<table><caption>Table 6: ERA5 file content</caption><tr><td>acquisition_time</td><td>time of acquisition<br/>written as double, 2D matrix dim=584x1388</td></tr><tr><td>lat</td><td>latitude in degrees<br/>written as float, 2D matrix dim=584x1388</td></tr><tr><td>lon</td><td>longitude in degrees<br/>written as float, 2D matrix dim=584x1388</td></tr><tr><td>2m温度</td><td>2-meter air temperatures<br/>written as double, 2D matrix dim=584x1388</td></tr><tr><td>soil temperature level_1</td><td>Soil temperature at level 1 (0-7cm)<br/>written as double, 2D matrix dim=584x1388</td></tr><tr><td>soil temperature level_3</td><td>Soil temperature at level 3 (50 cm depth)<br/>written as double, 2D matrix dim=584x1388</td></tr><tr><td>UW</td><td>Atmospheric Water Vapor<br/>written as double, 2D matrix dim=584x1388</td></tr><tr><td>surface pressure</td><td>atmospheric pressure at surface level</td></tr><tr><td>skin temperature</td><td>written as double, 2D matrix dim=584x1388<br/>soil skin temperature<br/>written as double, 2D matrix dim=584x1388</td></tr><tr><td>volumetric soil water layer_1</td><td>surface soil moisture<br/>written as double, 2D matrix dim=584x1388</td></tr></table>
# 4 VOD Output Data file

The last products to be detailed are the output products containing the VOD. Every band is reported as separate files, as well as the orbits which are distinguished between ascending and descending. Note that the ascending/descending orbits do not correspond for SMOS and AMSR-E/2.

## 4.1 Naming convention

The files are named such as: **OSMOSE_XXXX_F_O_YYYYMMDD_001.nc**
with each item corresponding to

* OSMOSE: Optical SMOS Experiment, specifies that the ERA5 specifically processed for the OSMOSE project

* XXXX: instrument, can be either SMOS, AMSRE, or AMSR2.

* F: letter relative to the frequency band; can be either L, C or X

* O: stands for the orbit overpass, Ascending or Descending

* YYYY: 4-digit for year

* MM: 2-digit for month

* DD: 2-digit for day

* 001: number of times the product has been created
## 4.2 file content

<table><caption>Table 7: VOD file content</caption><tr><td>lat</td><td>latitude in degrees<br>written as double, vector dim=1x584</td></tr><tr><td>lon</td><td>longitude in degrees<br>written as double, vector dim=1x1388</td></tr><tr><td>Soil_Moisture</td><td>Surface Soil Moisture, in m<sup>3</sup>.m<sup>-3</sup><br>written as double, 2D matrix dim=584x1388</td></tr><tr><td>Soil_Moisture_StdError</td><td>Soil moisture range due to modeling uncertainties, in m<sup>3</sup>.m<sup>-3</sup><br>written as double, 2D matrix dim=584x1388</td></tr><tr><td>Optical_Thickness_Nad</td><td>or VOD, transmittivity of vegetation layer at Nadir, unitless<br>written as double, 2D matrix dim=584x1388</td></tr><tr><td>Optical_Thickness_Nad_StdError</td><td>VOD range due to modeling uncertainties, unitless<br>written as double, 2D matrix dim=584x1388</td></tr><tr><td>Quality_Flag</td><td>0: data OK, 1: data not recommended, 2: missing data, unitless<br>written as byte, 2D matrix dim=584x1388</td></tr><tr><td>Scene_Flags</td><td>Scene Flags<br>written as byte, 2D matrix dim=584x1388</td></tr><tr><td>Processing_Flags</td><td>Processing Flags, unitless<br>written as byte, 2D matrix dim=584x1388</td></tr><tr><td>RMSE</td><td>RMSE between SMOS-TB and modeled TB, in Kelvin<br>written as double, 2D matrix dim=584x1388</td></tr><tr><td>Soil_TemperatureLEVEL1</td><td>ECMWF Soil Temperature at surface level 1, in Kelvin K.<br>written as double, 2D matrix dim=584x1388</td></tr><tr><td>Days</td><td>Number of Days since 1/1/2000<br>written as integer, 2D matrix dim=584x1388</td></tr><tr><td>UTC_Seconds</td><td>Number of Seconds of the day<br>written as integer, 2D matrix dim=584x1388</td></tr><tr><td>UTC_Microseconds</td><td>Number of Microseconds of the day<br>written as integer, 2D matrix dim=584x1388</td></tr><tr><td>RFI_ratio</td><td>Index to evaluate the impact of RFI, unitless<br>written as double, 2D matrix dim=584x1388</td></tr><tr><td>UTC_Minutes</td><td>Number of minutes since the start of the day<br>written as float, 2D matrix dim=584x1388</td></tr></table>

### RFI_ratio

RFI_ratio (Table 7) only concerns SMOS-derived VOD. It is computed by dividing the number of RFI flags per bin (from L1c data) by the number of TB per bin. Users can filter the derived SM/VOD based on this ratio of RFI by applying a user-defined threshold. For example, applying a threshold of 0.2 means that any SM/VOD retrievals associated with a RFI_ratio greater than 0.2 should be discarded from any analysis (i.e. more than 20% of the input brightness temperatures are tagged as contaminated by RFI).

### Scene_Flags

The Scene_Flags is a binary flag encoded on a byte that identifies moderate or strong topography, frozen soil (if soil temperature below 273K) or if a pixel is polluted by more than 10% of Water/Urban/Permanent Ice land cover types. The table 8 summarizes the flag signification per bit.
<table><caption>Table 8: Bit signification of the Scene_Flags</caption><tr><td>Bit</td><td>8</td><td>7</td><td>6</td><td>5</td><td>4</td><td>3</td><td>2</td><td>1</td></tr><tr><td>Flag</td><td>No Flag</td><td>No Flag</td><td>No Flag</td><td>No Flag</td><td>Frozen Soil</td><td>Polluted Scene</td><td>Strong Topography</td><td>Moderate Topography</td></tr></table>

<table><tr><td>Processing_Flag</td><td>The Processing Flag is set to one when the RMSE between the modeled TB and the measured TB is above 12K.</td></tr><tr><td>Quality_Flag</td><td>The Quality flag is set to 1 when a Scene_Flag is raised or the Processing_Flag is raised.</td></tr></table>

## Bibliography

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[6] K. Knowles, M. Savoie, R. Armstrong, and M. J. Brodzik. AMSR-E/Aqua Daily EASE-Grid Brightness Temperatures. Technical report, NASA National Snow and Ice Data Center, Boulder, Colorado USA, 2006, Accessed April 2023. version 1. doi:10.5067/XIMNXRTQVMOX.

[7] NSIDC National Snow and Ice Data Center. AMSR-E/Aqua Data Quality and Data Uncertainty. Technical report, National Snow and Ice Data Center, University of Colorado, Boulder, 2014. URL: https://nsidc.org/sites/default/files/amsre-dataquality-datauncertainty.pdf.

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