Accurate and Robust Sensing of the Ionosphere With Uncoded Long Pulse ISR Measurements: 1‐Lag Profile Inversion of Ion Composition and Temperature

Abstract Incoherent scatter radar probing of the topside F‐region ionosphere with reduced electron densities residing at relatively large radar ranges requires the use of uncoded long pulse (ULP) transmissions. In these ULP measurements the range resolution is necessarily poor, rendering the inference of ionospheric state parameters such as composition, temperature, and drift velocity challenging. Specifically, accurate estimation of composition and temperature is crucial for determining the differential velocity measurements of topside constituents; a topic that is addressed in further detail in a companion paper. In this paper, we describe approaches to accurate and efficient estimation of plasma composition and temperature using long pulses. The first approach is based on the deconvolution of the lag profile matrix generated from ULP measurements, aiming to mitigate the range mixing effect due to the low range resolution. By exploiting the singular value decomposition of the range mixing ambiguity matrix, a data‐independent strategy is used to determine the regularization parameter for the deconvolution. The second approach is based on a correction of the lag‐dependent height offset errors by re‐aligning each column of the lag profile matrix to its proper height. These strategies are tested and compared through a synthetic test and validated with experimental data collected from Arecibo over a 63‐hr‐long observation interval in September 2016. Results show that these strategies are effective in mitigating the range mixing inherent in estimating ionospheric state parameters by spectral fitting.