Remote sensing instrumentation for volcanic ash clouds

Transcription

1 Remote sensing instrumentation for volcanic ash clouds Dr. Adam J. Durant Norwegian Institute for Air Research Fred Prata1,2, Cirilo Bernardo1, and Ian Davies3 1. Norwegian Ins;tute for Air Research, Norway 2. Nicarnica AS, Norway 3. easyjet, Plc., Luton, UK 22 March 2011

2 Volcanic ash ELEMENTS, VOL. 6, PP (Durant et al., Elements, 2010) 22 March 2011 IAGOS Technical Experts Workshop on Volcanic Ash- Clouds 2

3 Ash cloud encounters reported incidents between aircra\ and volcanic clouds 73 % are confirmed ash encounters 61 % involved airframe or engine damage 9 incidents resulted in engine shut- down during flight Average rate of 2 incidents/year since 1976 Most damaging incidents <1000 km from source volcano <24 hours a:er erup<on onset Guffan;, Marianne, Casadevall, T.J., and Budding, Karin, 2010, Encounters of aircra\ with volcanic ash clouds; A compila;on of known incidents, : U.S. Geological Survey Data Series 545, ver. 1.0, 12 p., plus 4 appendixes including the compila;on database [hgp://pubs.usgs.gov/ds/545/]. 22 March 2011 IAGOS Technical Experts Workshop on Volcanic Ash- Clouds 3

4 Outline Review of ash detec;on techniques In situ versus remote sensing Thermal infrared remote sensing Satellite- and ground- based Airborne Volcanic Object Imaging Detector 22 March 2011 IAGOS Technical Experts Workshop on Volcanic Ash- Clouds 4

5 In situ versus remote sensing In situ Instrumenta;on located at the point of interest and in contact with the subject of interest Remote sensing Instrumenta;on located some distance away from the subject of interest Passive or ac;ve 22 March 2011 IAGOS Technical Experts Workshop on Volcanic Ash- Clouds 5

6 Ash detection from aircraft Direct visual observation of volcanic ash cloud from the ground is very much dependent on the observer having prior knowledge that a volcanic eruption has occurred in the vicinity... Once the umbrella region has spread at high levels some distance from the volcano, however, it becomes increasingly difficult to discriminate from ordinary high (ice crystal) cloud. Generally, the high level veil of ash tends to dilute the yellowish colour of the sun, so that it appears very pale with brownish- or greyish-tinged edges. ICAO Manual on Volcanic Ash, Radioactive Material and Toxic Chemical Clouds (2007) 22 March 2011 IAGOS Technical Experts Workshop on Volcanic Ash- Clouds 6

7 Visual observation Schumann et al., 2010: ACPD 10, March 2011 IAGOS Technical Experts Workshop on Volcanic Ash- Clouds 7

8 FALCON lidar 2 May 2010 Light Detec<on And Ranging Detec;on limit: AOD < 0.01 Spa;al resolu;on: <4-60 m Nominal par;cle size sensi;vity: <0.1-2 μm Schumann et al., 2010: ACPD 10, March 2011 IAGOS Technical Experts Workshop on Volcanic Ash- Clouds 8

9 Radar Radio Detec<on And Ranging Keflavik Spa;al resolu;on: m- 10s km Nominal par;cle size sensi;vity: par;cle radius >>50 microns 22 March 2011 IAGOS Technical Experts Workshop on Volcanic Ash- Clouds 9 (Lacasse et al., 2004)

10 Satellite TIR remote sensing Ash par;cle IR absorp;on increases with λ between μm T c T s I i B(T s ) > B(T c ) I i e τ i B(T s ) + (1 e τ i )B(T c ) I i - measured radiance at λ i T s - surface temp T c - cloud temp B - Planck function τ i - cloud optical depth Satellite- based TIR remote sensing Detec;on limit: <0.5 mgm 3 Spa;al resolu;on: <100 m 100s km Nominal par;cle size sensi;vity: < μm τ i > 1 I i B(T c ) τ i < 1 B(T s ) >> B(T c ) I i e -τi B(T s ) (Prata, 1989) 22 March 2011 IAGOS Technical Experts Workshop on Volcanic Ash- Clouds 10

11 T 11μm T 12μm Theore;cal behaviour of spherical water droplets with radii >50 µm Theore;cal behaviour of spherical silicate par;cles with radii 1 10 µm 22 March 2011 IAGOS Technical Experts Workshop on Volcanic Ash- Clouds 11

12 Ground-based IR camera NicAIR ( Func;on of par;cle radius (r), infrared op;cal depth (τ), and zenith viewing angle (θ) for a volcanic cloud with uniform temperature Tc and a background temperature Tb Correct for water vapour absorp;on (greatest near surface) Ground- based TIR remote sensing Detec;on limit: <0.2 mgm 3 Spa;al resolu;on: 1-10 m Nominal par;cle size sensi;vity: < microns 22 March 2011 IAGOS Technical Experts Workshop on Volcanic Ash- Clouds 12 Prata, A. J., and C. Bernardo (2009), JVGR 186.

13 Techniques summary Method Op;cal par;cle counter Detec<on limit Resolu<on Lidar AOD <0.01 <4 60 m ver;cal resolu;on Nominal par<cle size sensi<vity Limita<ons mm ~ μm Sampling bias; par;cle shape effects; uncertainty in refrac;ve index; Radar m 10s km Par;cle radius: >50 μm (Ka band) mm (X- band) Satellite TIR RS Surface TIR RS <0.5 mgm 3 (1 km thick layer) <0.2 mgm 3 (PL ~1 km) <100 m 100s km 1-10 m <0.1 2 μm Maximum size smaller than typical ash size; sunlight decreases SNR; hydrometeors prevent measurements; complicated retrieval Effec;ve radius: μm Effec;ve radius: μm Agenua;on by water clouds; minimum size larger than typical ash size; Op;cally thick cloud or hydrometeors complicates retrieval; uncertainty in par;cle refrac;ve index Op;cally thick cloud or hydrometeors complicates retrieval; uncertainty in par;cle refrac;ve index 22 March 2011 IAGOS Technical Experts Workshop on Volcanic Ash- Clouds 13

14 Key requirements of an airborne system Dis;nguish between water clouds, airborne dust par;cles and volcanic ash par;cles Provide measure of airborne ash abundance Provide rapid informa;on on ash cloud loca;on Aircra\ moves at >800 km/h at cruising speed Translates to ~7.5 minutes warning to target 100 km from aircra\ Provide cloud height and thickness data 22 March 2011 IAGOS Technical Experts Workshop on Volcanic Ash- Clouds 14

15 Summary Approach Measurement Loca<on Opera<onal applica<on Aircra: naviga<on In situ, e.g., CAPS probe point At loca;on of measurement 1. Measure of aircra\ exposure Execute ash- cloud encounter maneuver Remote sensing, e.g., AVOID pathlength integrated Up to 100s km from target 1. Dis;nguish ash and water clouds 2. Measure of poten;al dose along aircra\ trajectory Up to minutes warning execute change of course maneuver to avoid ash- cloud encounter 22 March 2011 IAGOS Technical Experts Workshop on Volcanic Ash- Clouds 15