# The Use of SMAP-Reflectometry in Science Applications: Calibration and Capabilities
## 5 Discussion  
The calibration of the SMAP-R dataset is a key step in the production and delivery of this data to the scientific community. Results show that when using the peak SNR of the DDMs alone, the differences between using the calibrated and the uncalibrated SMAP-R data can be up to 12 dB for samples with incidence angles below \(38.4^{\circ}\) and over \(41.6^{\circ}\). This effect is even more critical in the delay and Doppler bins further away from the peak one. We demonstrated that those differences have an impact on the sensitivity to different geophysical parameters, which can mislead the results obtained in scientific research.  
The characteristics of SMAP-R, such as its high antenna gain, polarimetric measurements (H and V polarizations), and polar coverage, provide the capability to study cryosphere, land, and ocean processes such as sea ice properties, land surface, freeze/thaw state, freeze/thaw seasonal transition, and vegetation water content. The low integration times characteristic of SMAP-R measurements could also benefit studies related to oil slick detection, which are characterized by highly coherent signatures over the ocean surface, but the low temporal coverage reduces the possibility to observe such events. SMAP-R could also enhance studies of wetlands and inundation. The availability of raw data also opens the possibility for analysis of the phase of the measurements. For example, highly coherent surfaces such as the sea ice will allow phase altimetry studies to determine the thickness of the ice [17]. The greatest challenge is the low sampling and low coverage of SMAP-R, which limits  
Figure 21: Standard deviation representing the spatial variability observed for February 2018 data: (**a**) uncalibrated V-pol, (**b**) calibrated V-pol, (**c**) uncalibrated H-pol, and (**d**) calibrated H-pol. The spatial variability is analyzed in \(1^{\circ}\times 1^{\circ}\) boxes (lat/lon). Note that calibrated values correspond to radar cross section values after applying calibration Equation (5), under coherent assumption.  
some of the applications requiring high repeatability and daily coverage over small areas (such as flooding or oil slicks). Other applications that do not require high temporal repeat over small areas can be addressed through observational strategies by averaging data over longer periods of time (15 days to 1 month) to obtain two state extremes for a given geophysical parameter and analyzing the seasonal transitions between states.  
SMAP-R is a great asset for understanding the capabilities that global L-band polarimetric measurements can bring to the scientific community. SMAP-R is based on forward scattering, which could complement future active radar satellite missions such as the NASA-ISRO SAR Mission (NISAR, [45]). NISAR is a joint SAR satellite mission between NASA and the Indian Space Research Organization (ISRO) that is optimized for studying hazards and global environmental change. It will measure backscatter at L- and S-bands at dual polarization, with polar coverage and will provide 12 days exact repeat cycles with a spatial resolution of 3-10 m (mode dependent). Daily updates from SMAP-R can be used to fill in the gaps between NISAR repeat cycles. SMAP-R is also a great asset towards the development of future GNSS-R missions, by informing on the potential of polarimetric measurements, global coverage, phase information, higher SNRs, and reduced integration times.