  How the solar corona is heated to high temperatures remains an unsolved
mystery in solar physics. In the present study we analyse observations of 50
whole active-region loops taken with the Extreme-ultraviolet Imaging
Spectrometer (EIS) on board the Hinode satellite. Eleven loops were classified
as cool (<1 MK) and 39 as warm (1-2 MK) loops. We study their plasma parameters
such as densities, temperatures, filling factors, non-thermal velocities and
Doppler velocities. We combine spectroscopic analysis with linear force-free
magnetic-field extrapolation to derive the three-dimensional structure and
positioning of the loops, their lengths and heights as well as the magnetic
field strength along the loops. We use density-sensitive line pairs from Fe
XII, Fe XIII, Si X and Mg VII ions to obtain electron densities by taking
special care of intensity background-subtraction. The emission-measure loci
method is used to obtain the loop temperatures. We find that the loops are
nearly isothermal along the line-of-sight. Their filling factors are between 8%
and 89%. We also compare the observed parameters with the theoretical RTV
scaling law. We find that most of the loops are in an overpressure state
relative to the RTV predictions. In a followup study, we will report a heating
model of a parallel-cascade-based mechanism and will compare the model
parameters with the loop plasma and structural parameters derived here.
