Adv. Space Res. Vol. 7, No. 11, pp. (11)305—(11)308, 1987 0273—1177/87 80.00+50 Printed in Great Britain. All rights reserved. Copyright © 1987 COSPAR X-BAND FEATURES OF CANOPY COVER: AN UP TO DATE SUMMARY OF ACTIVE AND PASSIVE MEASUREMENTS S. Paloscia and P. Pampaloni C.N.R. Via Pian dei Giullari, 42 -50125 Firenze, Italy ABSTRACT In this paper we summarize the results of investigations carried out on vegetation in the last five years using active and passive X band sensors. These results show that, although the sensitivity of passive systems to different types of vegetation is rather low, crop classification by means of X band radar has promising applications. Moreover, the measure- ments have shown that very sensitive radiometers can detect plant moisture and a relationship between plant water content and the optical depth has been found using a model based on Radiative Transfer theory. Finally, the backscattering coefficients of certain crops have been computed from radiometric data through a model developed by Tsang. INTRODUCTION Microwave (MW) observations at X band seem to have promising applications for land mapping and crop classification. Some interesting preliminary results have been obtained using ground based scatterometers and airborne real or synthetic aperture radars. Future plans in space activity consider X band of great interest for land applications: German—Italian cooperation for the X SAR (SIR C) as well as ESA proposals for a land application advanced satellite and the Agrisar campaign are good examples. This survey of vegetation X band features is intended to give a contribution towards optimal planning of future programs and scheduling of the X SAR experiments. Remote sensing research began in Florence about 7 years ago and since 1980 several observations have been carried out in agricultural fields /1/. This activity can be summarized as follows Active systems: SAR 580 Campaign (1981) on the test site in Southern Tuscany. Ka band back— scattering measurements using a ground based scatterometer. Agrisar Campaign (1986) on the “Oltrepô Pavese” test site (North Italy). Passive systems: X and Ka band observations using ground based sensors on several test sites in Italy (Puglia, Southern Tuscany, Northern Tuscany) and France (Toulouse) (1980—84). Air- borne X and Ka band observations (1986) on the “Oltrepô Pavese” test site (North Italy). Combined active and passive: Simultaneous observations at Ka band in Italy and France and at X band in Italy for Agrisar (1986). Main investigated crops were: corn, alfalfa, wheat and pasture. Only X band observations are considered in this work. The first part of this paper is an example of the utilisation of Radar data in crop classi- fication; for this study an one look image, collected during the SAR 580 Campaign, has been used. Although SAR is probabily the most useful microwave sensor for practical applications and mainly for land mapping and crop classification, the extraction of certain geophysical parameters, such as soil moisture, plant water content or leaf area index, requires proved models and accurate calibration. On the other hand, passive sensors are simpler, less expen- sive and easier to use, moreover radiometric features are chiefly important in understanding the interaction mechanism of microwaves and terrain and therefore, provided adequate models are available, radiometers can give significant contributions in radar data interpretation and in radar calibration, too. The second part of this paper is devoted to crop emissivity and its interdependance with plant water content. Finally, the relationship between emission and the scattering properties of vegetation is considered using a model developed by Tsang et al. /2/. (11)305