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In the 2016 observational context, appropriate choices are as follows.

For atomic species, use optical transit spectra of Na I near $0.589\mu \mathrm{m}$ and K I near $0.770\mu \mathrm{m}$, with Hubble Space Telescope/STIS or ground-based high-resolution instruments on Very Large Telescope/Keck telescope-class telescopes. Neutral/ionized ultraviolet metal lines offer additional diagnostics with Hubble Space Telescope. Resolving a line's shape and distinguishing stellar contamination matters as much as locating its wavelength.

For molecules, use near/mid-IR spectroscopy: water bands near $1.4$, $1.9$ and $2.7\mu \mathrm{m}$, CO near $2.3$ and $4.6\mu \mathrm{m}$, methane near $3.3\mu \mathrm{m}$, and ${\mathrm{CO}}_2$ near $4.3$ or $15\mu \mathrm{m}$. Hubble Space Telescope/WFC3 samples water around $1.1$--$1.7\mu \mathrm{m}$; ground-based Very Large Telescope/CRIRES or Keck telescope/NIRSPEC spectra target accessible near-IR windows such as CO at $2.3\mu \mathrm{m}$. Warm Spitzer Space Telescope provides $3.6$ and $4.5\mu \mathrm{m}$ photometry, while cryogenic Spitzer Space Telescope spectra/longer-wavelength data are archival by 2016. A broadband eclipse point alone does not uniquely identify a molecule.

For atmospheric escape, use ultraviolet transit spectroscopy of H I Ly$\alpha$ at $121.6\mathrm{nm}$, and suitable C/O/metal lines, with Hubble Space Telescope/STIS or COS. Extended, velocity-shifted absorption beyond the optical planet suggests an escaping envelope, although stellar variability, geocoronal emission and interstellar absorption require treatment. Ground-based H$\alpha$ at $656.3\mathrm{nm}$ probes excited hydrogen and is a complementary rather than interchangeable measure of neutral-hydrogen escape.

Three complementary methods available in the setting of this 2017 paper are:

Transmission probes the limb, eclipses probe the dayside, and direct imaging isolates spatially resolved planetary light. Radial velocities alone measure orbital motion rather than atmospheric composition; high-resolution planetary Doppler spectroscopy can instead detect atmospheric spectral lines if planetary light is isolated statistically.

Three complementary approaches replace the simple thick solid disk:

“Operational” and “planned” here refer to the 2018 examination date. The next generation included the 39-metre Extremely Large Telescope with 798 segments, the thirty-metre Thirty Meter Telescope with 492 segments, and the Giant Magellan Telescope using seven 8.4-metre primary mirrors. These designs extend segmentation or lightweight casting with active control, rather than simply making a thicker slab. The specifications are documented by the 2017 ELT announcement, TMT optics design and GMT primary-mirror description. Adaptive optics is also needed to exploit the large apertures against atmospheric turbulence; it corrects faster disturbances than active optics.

First refine the ephemeris, planetary mass, stellar radius, and stellar variability using exoplanet transit photometry and the radial-velocity method. Then combine observations that probe different regions rather than relying on one spectrum. A present-day programme could use the following complementary measurements; in the 2019 setting of the paper, James Webb Space Telescope observations would have been a future capability.

Together these address aerosols, molecular composition, elemental enrichment, vertical thermal structure, horizontal heat transport, winds, and escape. Repeat key events and monitor stellar activity, since stellar contamination and instrumental trends can imitate atmospheric signals. Use actual brightness, saturation limits, and predicted feature amplitudes to choose observing modes and exposure times.

The wavelength ranges and time-series capabilities are documented in the NIRISS SOSS guide, NIRSpec overview, MIRI spectroscopy guide, and ESO's CRIRES description.