Definition of Calibration Terms

Transcription

1 Microwaves and Radar Institute Tandem-L, Technical Note Doc. No.: TDL-SE-TN-0010 prepared: J. Reimann, M. Schwerdt Date Calibration Engineer reviewed: M. Schwerdt Date Head of Calibration Group released: M. Zink Date Project Manager Restriction of Disclosure: All rights reserved. No part of this document may be reproduced, in any form or by any means, without permission in written form by the Tandem-L Project Manager of the German Aerospace Center (DLR)

2 Page: 2 of 9 Document Preparation The document on hand was prepared with contributions from the personnel listed below: Name (name, surname) Organizational Unit Microwaves and Radar Institute (DLR-HR) Jens Reimann DLR-HR-STL Patrick Klenk DLR-HR-STL Marco Schwerdt DLR-HR-STL Custodian of this document is: J. Reimann Distribution This document is stored on the Tandem-L Project Server. It is accessible to all participants of the Tandem-L Project. Documents classified as Public may be distributed outside the Tandem-L project team. Documents classified as Project Internal may only be distributed to the Tandem-L project team including project members of external organizations or companies. Documents classified as DLR Project Internal may only be distributed to the DLR Tandem-L project team.

3 Page: 3 of 9 Document Change Control This document is under configuration control. Latest changes to the document are listed first. Issue Date Chapter Changes All First issue Note: Verify that this is the correct revision before use. Check the document server for the latest version. Hardcopies of distributed documents are not updated automatically.

4 Page: 4 of 9 Table of CONTENTs 1 Introduction Purpose and Scope General Terms Accuracy Definition Verification Dynamic Range Definition Verification Radiometric Calibration Terms Radiometric Stability Definition Verification Remarks Absolute Radiometric Accuracy Definition Verification... 9

5 Page: 5 of 9 References Applicable References The following documents are fully applicable together with this document. Document ID Document Title Issue [A-1] TDL-MD-DD-0002 Mission Description Document v1.0 [A-2] TDL-MD-RD-0003 Mission Requirements Document v1.0 [A-3] Pre-Phase-A Status Report v1.0 Normative References The following standards have been used for preparing the document on hand (e.g. ECSS). [N-1] [N-2] [N-3] Document ID Document Title Issue Informative References The following documents, though not formally part of this document, amplify or clarify its content. Document ID Document Title Issue [I-1] TDL-MD-RD-0001 User Requirements Document v1.0 [I-2] [I-3]

6 Page: 6 of 9 Terms, Definitions and Abbreviations Note: Terms, definitions and abbreviations with relevance to the overall project are to be entered into the central project glossary maintained on the Project Server under Terms. Terms, definitions and abbreviations with no relevance to the overall project, but necessary to understand the document on hand, may be listed below. Terms and Definitions Term Definition Abbreviations Abbreviation PRI RCS SAR Meaning Pulse Repetition Interval Radar Cross Section Synthetic Aperture Radar

7 Page: 7 of 9 1 Introduction 1.1 Purpose and Scope For a mission like Tandem-L it is essential to have common understanding on requirements and their meaning. Hence a clear definition of terms is required. This document compiles terms and their verification strategy related to the calibration of the SAR instrument.

8 Page: 8 of 9 2 General Terms 2.1 Accuracy In metrology accuracy is defined as the difference between measured value and true value. For any practical measurement the true value is not known and hence the accuracy cannot be stated. The term uncertainty shall be used instead. It describes the confidence of a measurement without any assertion to the true value. To avoid any confusions to the end users of SAR product (which may not even care about the difference between accuracy and uncertainty) the term accuracy will be kept, but redefined to essentially match the term uncertainty. Throughout this document the term accuracy will be used as a drop-in replacement of uncertainty Definition Accuracy is defined as the remaining uncertainty after correcting for all known systematic effects Verification Not applicable. 2.2 Dynamic Range Definition The Dynamic Range is defined as the range of σ 0 values of an image target at level 1b measurable by the instrument within its specified radiometric, resolution and geometric accuracy and within the specified operational conditions without considering ambiguities. The instrument shall have a linear transfer function within the specified dynamic range Verification TBD

9 Page: 9 of 9 3 Radiometric Calibration Terms 3.1 Radiometric Stability Definition The standard deviation of repeated radar cross section or backscatter coefficient measurements of one or a series of targets located on the Earth s surface and acquired within the specified operational conditions, sufficiently sampled over a given time span T is called Radiometric Stability over T. The time span T is sufficiently sampled if all characteristic variations over T are captured Verification The Radiometric Stability is to be verified using one or a series of calibration targets considering their variability and stability. The radiometric stability shall only be verified at one point within the dynamic range of the SAR instrument which is of such magnitude that the receiver noise is insignificant. The variability is defined for point targets as the difference of RCS between several targets and for isotropic distributed targets as the spatial homogeneity of backscatter Remarks Several requirements may be necessary for different time scales e.g.: Fast time (across range line, one PRI, e.g. S-1: gain variation over receive window) Slow time (across a synthetic aperture) Short term (within a scene) Inter orbit (changes within one orbit, e.g. long data takes) Inter repeat cycle (within a repeat cycle) Seasonal (sun dependent changes) Long term (timespan between two external calibration campaigns, e.g. due to aging effects) 3.2 Absolute Radiometric Accuracy Definition The Absolute Radiometric Accuracy is defined as the 1-sigma deviation resulting from measurements of targets with known radar cross section or backscattering coefficient with the instrument working in its specified operational conditions. The target may be located anywhere within the swath, at any point within the orbit and has to be of such magnitude that the receiver noise is insignificant Verification The Absolute Radiometric Accuracy is to be verified using one or a series of calibration targets with known absolute RCS. The absolute radiometric accuracy shall be verified at least at one point within the dynamic range of the SAR instrument. Point targets must provide a signal to clutter ratio sufficient to allow the verification of the absolute radiometric accuracy requirement.