935 
1. Beijing 2008 
THE AEROSPACE IMAGING INTERFEROMETER ALISEO: FURTHER 
IMPROVEMENTS OF CALIBRATION METHODS 
AND ASSESSMENT OF INTERFEROMETER RESPONSE 
A. Barducci, F. Castagnoli, G. Castellini, D. Guzzi, P. Marcoionni, *1. Pippi 
CNR - IFAC 
Via Madonna del Piano 10, 50019 Sesto Fiorentino, ITALY 
Tel.: +39 0555226301, Fax: +39 0555226348, *e-mail: I.Pippi@ifac.cnr.it 
Commission I, WG-I/6 
KEY WORDS: Fourier transform imaging spectrometers, Sagnac interferometer, Optical calibration procedure, Remote sensing, 
Small-micro satellite. 
ABSTRACT: 
ALISEO (Aerospace Leap-frog Imaging Stationary Interferometer for Earth Observation) belongs to the stationary interferometers 
representing a promising architecture for future Earth Observation (EO) sensors due to their simple optical layout. ALISEO has been 
selected by the Italian Space Agency as the principal payload for a new optical mission based on a micro-satellite (MIOsat). 
Payloads planned for MIOsat are an extensible telescope, a high-resolution panchromatic camera, a Mach-Zehnder MEMS 
interferometer, and ALISEO. MIOsat platform is expected to provide the payloads with sight steering capability, in order to mitigate 
the sensor’s data-rate and improve the integration time. ALISEO operates in the common-path Sagnac configuration, and it does not 
employ any moving part to generate phase delay between the two rays. The sensor acquires the target images modulated by a pattern 
of autocorrelation functions: a fringe pattern that is fixed with respect to the instrument’s field of view. The complete interferogram 
of each target location is retrieved introducing relative source-observer motion, which allows any image pixels to be observed under 
different phase delays after moving thorought the sensor’s field of view. In this paper we discuss some experimental and theoretical 
investigations concerning ALISEO’s architecture and performance. We describe recent advances in the optical layout selected for 
the sensor, as well as the outcome of simulations of its main chasracteristics. In order to refine the calibration of the optical path 
difference (OPD) of raw interferograms a new data-processing procedure has been developed, based on a set of measurements have 
been carried out using a double planar diffuser system and several coloured He-Ne lasers. Standard reflectance tiles have been used 
for validating the wavelength calibration of the instrument, hence proving the reliability of the reflectance retrieving procedure. 
1. INTRODUCTION 
Our Institute was appointed by the Italian Space Agency (ASI) 
to carry out a feasibility study to determine the optimal 
characteristics of a space qualified version of an imaging 
interferometer to be placed on board of a micro-satellite in a 
low.cost mission. 
A valuable advantage of imaging interferometers is their ability 
to change the sampled spectral range and their resolving power 
by simply adjusting the sensor sampling step and the instrument 
Field-Of-View (FOV) (Hamisch, 2002; Jacquinot, 1954; 
Griffiths, 1977). An additional advantage is connected with the 
possible exclusion of the input slit, which strongly reduces the 
radaint power admitted in dispersive spectrometers. Critical 
points are associated with the heavy data pre-processing 
necessary for compensating the instrument response and 
possible acquisition artefacts (Persky, 1995). Moreover, due to 
the nature of the acquired interferogram it is crucial adopting 
detectors with high accuracy of digitalisation (Sellar, 2003). 
Our study leaded to the development of ALISEO (Aerospace 
Leap-frog Imaging Stationary interferometer for Eath 
Observation) and ASI selected it as the main payload for the 
first optical small mission based on a new micro-satellite 
(MIOsat). Other payloads are a panchromatic camera and a 
MEMS interferometer for atmospheric sounding. All the 
activities related to this space mission have been started on 
May 2007.. 
The mission and payload requirements are listed in the tables 1 
and 2. 
MIOsat operational characteristics 
Orbit 
polar, sun-synchronous 
Descending node 
9:30 - 10:30 a.m. local time 
Altitude 
500 Km 
Expected life-time 
2-3 years 
Size 
lm x lm x lm 
Mass 
Less than 130 Kg 
Power 
Less than 150 W 
Table 1. MIOsat mission characteristics 
The paper describes the main characteristics of the prototype 
imaging interferometer developed at our Institute, moreover 
some theoretical issues concerning sampling theory in 
“common path” imaging interferometry are investigated. The 
procedures for extracting pixel interferograms from a complete 
set of images and the methods for calibrating the instrument 
response are presented in section dedicated to Experimental 
Activity together with some experimental results. Finally the 
outcomes from our investigation are summarized together with 
open problems and future work.