The Microwave Imagine Radiometer with Aperture Synthesis (MIRAS) aboard the SMOS satellite measures the Earth's surface brightness temperature at L-Band at a frequency of 1.4 GHz. These measurements are full polarimetric and are carried out at nadir incidence angles of between 0 and 65°. Both polar hemispheres are covered completely every day.
Here we offer mean daily brightness temperature intensities gridded onto a polar-stereographic grid with 12.5 km grid resolution. In order to do so, first all brightness temperature (TB) measurements carried out during one day at both polarizations (horizontal and vertical, h and v) and nadir incidence angles of between 0 and 40° are collected on the special SMOS ISEA grid (The special viewing geometry of SMOS required a special native grid.). TBh and TBv have to acquired within 2.5 s to form a data pair to be used. For each SMOS ISEA grid cell all TB values are averaged over the given incidence angle range to compute the brightness temperature intensity (TBh + TBv)/2. Subsequently, the data are interpolated onto the mentioned polar-stereographic grid.
The documentation reveals more details of the processing.