Remote sensing is based on the ability to measure accurately the spectral radiance of remote objects in the object plane. This ability is limited by the measuring system (resolution and sensitivity) and by the atmospheric transmittance, especially when long distances are involved. As a result, the need to enhance S/N led us to develop new measurements techniques and analysis methods. This presentation deals with two different techniques of modern radiometry -- point spectroradiometry with moderate spectral resolution and spatial radiometry (imaging systems) with low spectral resolution. This presentation will address three issues related to advanced analysis methods of radiometric measurements: (1) The effect of the exact shape of the slit- function of the point radiometer on the results of the spectral analysis, (2) the optimal calculation of a signature from radiometric imager, and (3) the correcting factor that must be introduced into the analysis of a spatial picture of point target which is much smaller than the IFOV of the imaging system (star detection). The experience and knowledge gained by IMOD and EORD in the area of radiometric analysis was implemented in a user friendly software (TIRAS) that is used for the radiometric (and not temperature) analysis of various spatial radiometers. The radiometric data was measured for various applications of IMOD such as data bases of targets and backgrounds, and study of radiometric behavior of IR scene elements.
Passive MMW sensing is getting more and more attention as sensors in this spectral region get better. This development requires understanding of the passive MMW target detection scenario. This scenario consists of natural background elements and targets. Understanding of the behavior of backgrounds and targets as function of environmental conditions is vital for the analysis of any future sensor performance for this spectral region. During the past year, EORD has measured the radiometric properties of natural backgrounds and several man made objects using its dual frequency 140/220 GHz radiometer. This work will describe the measurement setup and give some of the results of background and target measurements. The measurement results will be correlated to the thermal IR radiometric data and the actual contact temperatures of the objects.
Knowledge of background properties is essential for various applications such as systems engineering and evaluation (e.g. electro-optical sensors or for camouflage design), operational planning and development of ATR algorithms. A series of field tests was conducted in the NEGEV desert in Israel, as a joint effort of the FGAN-FfO (Germany) and EORD (Israel) for characterizing properties of backgrounds in arid climatic regions. Diurnal cycles of background surface temperatures were measured during summer and winter periods in several sites in the NEGEV. The measurement equipment consisted of imaging cameras, most of them calibrated, covering the spectral region from the visible up to the thermal infrared. This paper presents the measurement set- up, the measurement techniques that were used, and some of the first analysis results.
The computer code LOWTRAN is widely and extensively used for the prediction of propagation of IR radiation through the atmosphere. The latest version of this code, LOWTRAN 7, is assumed to be the most elaborate and accurate one. Hence it was decided to test its validity by comparing its prediction for ground-to-space slant paths with actual transmittance measurements with the sun as a blackbody source. A good agreement between the theoretical predictions and the experimental results were obtained in the 8 - 12 micrometers spectral region for all zenith angles between 90 degree(s) and 60 degree(s) (0 degree(s) to 30 degree(s) above the horizon). In the 3 - 5 micrometers spectral region some spectral discrepancy was observed though the value of the integrated measured transmittance agreed well with the predicted one. The reasons for this can be assumed to be in the new band model absorption parameters (in the 3 - 4 micrometers region) and in the water continuum model (in the 4.4 - 5.2 micrometers region).
Background images of a typical Mediterranean landscape were measured for 24 hours and their properties were analyzed. The locations were chosen to represent an area with various amount of vegetation. The thermal mean and variance changes around the clock were extracted from these background images and a typical pattern for the variance behavior was identified. A simple model is suggested for describing this behavior. The knowledge of variance dependence on the scene and measurement system parameters could be further used for simulation of IR images or for detection probability estimation.
The factors affecting the spectral composition of radiation reaching a distant observer from a natural object, and thus determining its apparent color, are experimentally studied. A method to calculate the apparent color is examined in which the spectral radiance of a distant object is first measured at zero distance and variations in the apparent radiance are then studied as a function of the distance. Sample results are given.
Both the theoretical and the experimental problems of backgrounds are examined. The authors show why the current definitions of correlation length should be used with care, with attention paid to the intensity histogram of a scene. Different effects of the sub-pixel features in a measured scene on the clutter for imaging and scanning systems are also explained. The two- dimensional polarization of a scene is measured and found to compare favorably with the theoretical predictions. Finally, the authors show how to simulate backgrounds whose power spectrum is given, together with constraints on the image proper. This is achieved by iteratively transforming between the image plane and its Fourier conjugate, while imposing the appropriate constraints in both planes.
This work describes a new technique that can be used to determine the IR transmittance and path radiance of an obscuring atmosphere. The method is based on alternate measurements of contrast through a clear and obscuring atmosphere respectively. An advantage of this technique is that it utilizes existing thermal imagers and does not require an additional transmissometer in the field. The technique was tested using an AGEI4A 780 Thermovision camera operating in the 7.7-13.2 micron spectral region. A good agreement between theory and the experimental results was obtained.