AMSR2 IB X-VOD is a passive X-band vegetation optical depth (X-VOD) product retrieved from AMSR2 (the Advanced Microwave Scanning Radiometer 2) brightness temperature observations. It was developed by the INRAE-Bordeaux (IB) Remote Sensing Lab and based on the inversion of the X-MEB model (X-band microwave emission of the biosphere) (Wang et al., 2021). The X-MEB model is an extension of the L-MEB model (Wigneron et al., 2007; Fernandez-Moran et al., 2017) to the X-band.
Key Features:
(i) Only VOD was retrieved while SM was from a reanalysis data set (ERA5 data set); (ii) MPDI (the Microwave Polarization Difference Index) was used to initialize the cost function; and (iii) the values of the soil and vegetation parameters were calibrated for X-band.
Product:
AMSR2 IB X-VOD provides daily descending (overpass at 01:30 a.m. Local Solar Time) VOD in the NetCDF format with the spatial resolution of 0.25° and with the WGS84 project for 3 years (2014-2016). The global product is ongoing.
Naming convention:
GW1AM2_IB_VOD_YYYYMMDD_D_X_V1.nc
Satellite : GW1(GCOM-W1) / PM1(AQUA)
Sensor: AM2(AMSR2) / AME(AMSR-E)
Producer: IB (Fixed Value)
Product name: VOD (Fixed Value)
Observation time: YYYYMMDD (UTC time)
Orbit direction: D (Descending)
Frequency channel: X band
Version: V1
Data Format:
All data are saved as 32-bit single point numbers in NetCDF format. Each file contains a 720 by 1440 entry map.
lat: latitude (°)
lon: longitude (°)
Optical_Thickness_Nad_H: Vegetation optical depth
Error_H: simulated TBH – observed TBH
Quality_Flag:
Quality_Flag = 1: missing data because of no valid TB
Quality_Flag = 2: missing data because of no valid ERA5 data
Quality_Flag = 4: missing data because of water polluted or frozen
Data Filtering:
For VOD applications: Error_H should be <= 5 K and the normal range of VOD values is [0, 1.5].
Daily VOD values can be slightly negative. This is expected from the point of view of the minimization process. Daily negative values were not set to zero here as they can be used to compute yearly average. After yearly averaging, negative yearly median VOD values, should be set equal to zero. These values are mostly distributed in Barren areas.
References:
Wang, M., Fan, L., Frappart, F., Ciais, P., Sun, R., Liu, Y., … & Wigneron, J. P. (2021). An alternative AMSR2 vegetation optical depth for monitoring vegetation at large scales. Remote Sensing of Environment, 263, 112556. https://doi.org/10.1016/j.rse.2021.112556
Wigneron, J. P., Kerr, Y., Waldteufel, P., Saleh, K., Escorihuela, M. J., Richaume, P., … & Schwank, M. (2007). L-band Microwave Emission of the Biosphere (L-MEB) Model: Description and calibration against experimental data sets over crop fields. Remote Sensing of Environment, 107(4), 639-655. https://doi.org/10.1016/j.rse.2006.10.014
Fernandez-Moran, R., Al-Yaari, A., Mialon, A., Mahmoodi, A., Al Bitar, A., De Lannoy, G., … & Wigneron, J. P. (2017). SMOS-IC: An alternative SMOS soil moisture and vegetation optical depth product. Remote Sensing, 9(5), 457. https://doi.org/10.3390/rs9050457
Questions?
Email : jean-pierre.wigneron [at] inrae.fr or Mengjia.Wang [at] inrae.fr