The JWST Exposure Time Calculator (ETC) SOSS Spectral Extraction strategy is only used for the NIRISS single object slitless spectroscopy mode, and allows extraction of the signal to noise for 2 spectral orders that will be used for science observations.

NIRISS Single Object Slitless Spectroscopy (SOSS) covers the wavelength range 0.63 to 2.81 μm and has 2 spectral orders that are scientifically useful, with order 1 covering 0.83 to 2.81 μm and order 2 covering 0.63 to 1.26 μm. The SOSS Spectral Extraction strategy in the ETC provides an option to specify the order for which the signal-to-noise ratio should be reported (Figure 1). The 1^st and 2^nd orders overlap spatially in the long wavelength region (when default CLEAR is selected with GR700XD in the Instrument Setup tab). The Instrument Setup tab has the option to select the F277W filter to isolate the 1^st order spectrum in this overlap region. An error will be returned when selecting F277W filter for order 2.

SOSS offers full frame readout, two subarray options SUBSTRIPE96, SUBSTRIPE256, and four multistripe modes SUB17STRIPE, SUB60STRIPE, SUB204STRIPE, and SUB680STRIPE  that also appear under the subarray menu. The multistripe modes support observations of bright targets. FULL array, SUBSTRIPE256 and the multistripe modes sample spectral orders 1 and 2. SUBSTRIP96 captures only the 1st spectral order (an error will be returned when attempting to run a calculation with SUBSTRIP96 and order set to 2).

The readout pattern and subarray options are specified in the Detector Setup tab. Both NIS and NISRAPID are supported for full frame readout and for SUB17/60/204/680STRIPE_SOSS but only NISRAPID is supported when using either the SUBSTRIP256 or SUBSTRIP96 subarray. An error will be returned when selecting NIS readout and the SUBSTRIP256 or SUBSTRIP96 subarray.

The extraction height of the SOSS spectrum in the cross-dispersion direction is determined by the PSF. The PSF for NIRISS SOSS is extended due to slight defocus that is built-in to allow observations of bright targets without causing saturation. The sky background is extracted for the same aperture set by the PSF, and there is no contaminating background flux in this case. The sky background is set by the options under the Backgrounds tab.

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