Welcome to the  
SMAPEx-4 Archive
Soil Moisture Active Passive Experiment

Soil Moisture and Ocean Salinity (SMOS)

The SMOS satellite was launched on 2nd November 2009, making it the first satellite to provide continuous multi-angular L-band (1.4GHz) radiometric measurements over the globe. Over continental surfaces, SMOS provides near-surface soil moisture data at ~50km resolution with a repeat cycle of 2-3 days. The payload is a 2D interferometer yielding a range of incidence angles from 0° to 55° at both V and H polarisations, and a 1,000km swath width. Its multi-incidence angle capability is expected to assist in determining ancillary data requirements such as vegetation attenuation. This satellite has a 6:00am/pm equator overpass time (6:00am local solar time at ascending node). Due to the synthetic aperture approach of this satellite, brightness temperature observations will be processed onto a fixed hexagonal grid with an approximately 12km node separation. While the actual footprint size will vary according to position in the swath, incidence angle etc., it will be approximately 42km diameter on average. Campaigns for validation of SMOS retrieval algorithms were the focus of a separate project, the Australian Airborne Cal/val Experiments for SMOS (AACES), and in this project SMOS data over the SMAPEx-4 flight areas will be used to inter-compare with SMAP, Aquarius, and airborne brightness temperature observations and soil moisture retrievals. The features of SMOS are summarized below. SMOS data can be downloaded from ESA.




Microwave Imaging Radiometer using Aperture Synthesis (MIRAS) using passive microwave 2D-interferometer concept



Launch date

2nd, Nov. 2009

Design life

Minimum 3 years


Sun-synchronous, dawn/dusk, quasi-circular orbit at altitude 758km. 6.00am local solar time at ascending node.

Spacecraft operations control centre

CNES, Toulouse, France

Centre frequency (GHz)

1.413 (L-band; 21cm)

Band width (MHz)



H & V (polarimetric mode optional)

Incidence angle(°)


Swath (km)


Spatial resolution (km)

35 at centre of field of view

Radiometric resolution (K)


Temporal resolution

3 days revisit at Equator






Created: February 2016
Last Modified: June 2016
Maintainer: Xiaoling Wu, xiaoling.wu@monash.edu