You should note that SMAP products are in HDF5 (or .h5) format which are accessible through HDFView to learn data structure and their content. SMAP data (h5 files) could also be read in MATLAB where you can plot and work with the data. Here is a sample MATLAB code that I use for reading SMAP soil moisture data:

SMAP_data_dir = 'D:\research\SMAP_ET\SMAP_data\';

fname = [SMAP_data_dir,'SMAP_L3_SM_P_20150506_R13080_001.h5'];

a = h5info(fname);

% 2 "Groups"

a.Groups(1) % Metadata

a.Groups(2) % /Soil_Moisture_Retrieval_Data

a.Groups(2).Datasets

a.Groups(2).Datasets.Name % Found the one I wanted... soil_moisture

SMAP_mois = h5read(fname,'/Soil_Moisture_Retrieval_Data/soil_moisture');

SMAP_mois(SMAP_mois