NEWSIPS Manual Addendum

I. Effect of Temperature Variations on SWP Ripple Correction

As mentioned in the NEWSIPS manual, the blaze wavelength in the SWP high dispersion ripple correction varies with temperature. Increasing the temperature shifts the blaze wavelength to higher wavelengths causing a variation in the ripple correction across the order. This can result in changes to the ripple-corrected and absolutely-calibrated fluxes, particularly at the ends of the orders where the ripple correction is largest.

The temperature parameter used in the SWP ripple correction is the head amplifier temperature (THDA) as obtained at the end of the exposure. Because it is not certain how well this one temperature represnts the thermal conditions during each observation, it is possible that slight errors may be introduced. High dispersion SWP exposures obtained during large variations in spacecraft temperature may be most susceptible to this effect.

A study of how the magnitude of the THDA value can affect the SWP ripple-corrected and absolutely-calibrated fluxes showed that the temperature dependence increases with order number and is therefore most sensitive at the shorter wavelengths. Within a given order, the change in the ripple correction is 0 near the blaze wavelength and increases in magnitude toward the ends of the orders. A 1 degree error in THDA changes the ripple correction by a maximum of roughly 1% in order 80 (1740 A), 2% in order 100 (1390 A), and 3% in order 120 (1157 A). Figure 1 shows the variation in order 100 for THDA variations of 1 and 2 degrees C.

SWP ripple thda dependence

Figure1: Temperature Dependence for SWP Ripple Correction

last updated: 26 November 1997 rwt

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