Influence of the System MTF on the On-Board Lossless Compression of Hyperspectral Raw Data

• Main Authors: Bruno Aiazzi, Massimo Selva, Alberto Arienzo, Stefano Baronti
• Format: Article
• Language: English
• Published: MDPI AG 2019-04-01
• Series: Remote Sensing
• Subjects: Modulation Transfer Function (MTF); hyperspectral raw data; lossless compression; on-board real-time processing; spatial resolution; cut-off value; CCSDS compression standard; image acquisition noise; mini-satellites
• Online Access: https://www.mdpi.com/2072-4292/11/7/791

A noticeable topic to be pursued in the field of on-board real-time data processing is the influence of the modulation transfer function (MTF) of the image acquisition system on the lossless compressibility of raw (that is, uncalibrated) hyperspectral data. Actually, notwithstanding the system device is constrained by several design and manufacturing requirements, the impact of the on-board MTF on the performance of data compressors is becoming remarkable. In particular, the aim of reducing both transmission bandwidth/power and mass storage can be efficiently pursued. Such an analysis is expected to be useful especially for systems employed in mini-satellites, whose payload must be compact and light. From this perspective, this paper investigates the performance of a typical imaging system that acquires low/medium-spatial-resolution images, by considering high-resolution reference data, which simulate the real scene to be imaged. To this end, standard Consultative Committee for Space Data Systems (CCSDS) Aviris 2006 data have been chosen, due to their spatial resolution of <inline-formula> <math display="inline"> <semantics> <mrow> <mn>17</mn> </mrow> </semantics> </math> </inline-formula> m, which is adequate to be a reference for simulated data whose spatial resolution is foreseen between <inline-formula> <math display="inline"> <semantics> <mrow> <mn>50</mn> </mrow> </semantics> </math> </inline-formula> and <inline-formula> <math display="inline"> <semantics> <mrow> <mn>150</mn> </mrow> </semantics> </math> </inline-formula> m. MTF requirements are usually provided based on the cut-off value of the amplitude at the Nyquist frequency, which is defined as a half of the sampling frequency. Typically, a cut-off value between <inline-formula> <math display="inline"> <semantics> <mrow> <mn>0.2</mn> </mrow> </semantics> </math> </inline-formula> and <inline-formula> <math display="inline"> <semantics> <mrow> <mn>0.3</mn> </mrow> </semantics> </math> </inline-formula> ensures that a sufficient amount of information is delivered from the scene to the acquired image, by avoiding at the same time the degradation due to an excessive aliasing distortion. All the scores are achieved by running the standard lossless compression scheme CCSDS 1.2.3.0-B-1 for multispectral/hyperspectral data, as a function of the cut-off value and different noise acquisition levels. The final results, and related plots, show that this analysis can suggest a suitable choice for the cut-off value, to ensure both a sufficient quality and low bit rates for the transmitted data to the ground station.