How can I read the data ? What are the file formats ?

In each archive file (.tgz extension), there are two files

• A Header file (.HDR extension) : This is a text file, in XML Earth Explorer Header format

• A Data File (.DBL.nc extension) : This is a NetCDF file, format variant 2 (NetCDF 3 with 64-bit offset) or format variant 3 (NetCDF 4 classic model)

On the NetCDF website, there's a list of software for manipulating or displaying NetCDF Data :
https://www.unidata.ucar.edu/software/netcdf/software.html.