Mapping Vegetation with Synthetic Aperture Radar: Applications in Kenya and Southeast Asia Thomas Ballatore, Ph.D., GISP Director, Lake Basin Action Network Faculty Aide, Center for Geographic Analysis, Harvard University ABCD-GIS Seminar Series 07 December 2016 K450 CGIS Knafel

Remote sensing is… the practice of deriving information about the Earth’s land and water surfaces using images acquired from an overhead perspective, by employing electromagnetic radiation in one or more regions of the electromagnetic spectrum, reflected or emitted from the Earth’s surface. Campbell and Wynne Introduction to Remote Sensing p.6, 5th ed. (2011)

Remote sensing is… the practice of deriving information about the Earth’s land and water surfaces using images acquired from an overhead perspective, by employing electromagnetic radiation in one or more regions of the electromagnetic spectrum, reflected or emitted from the Earth’s surface. Campbell and Wynne Introduction to Remote Sensing p.6, 5th ed. (2011)

The Electromagnetic Spectrum CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=2521356

Sensing in the Visible and NIR http://landsat.gsfc.nasa.gov/wp-content/uploads/2015/06/Landsat.v.Sentinel-2.png

SPECTRAL Landsat OLI Soil Green Dry Soil Dry Green

The Problem with Clouds…

Remote sensing is… the practice of deriving information about the Earth’s land and water surfaces using images acquired from an overhead perspective, by employing electromagnetic radiation in one or more regions of the electromagnetic spectrum, reflected or emitted from the Earth’s surface. Campbell and Wynne Introduction to Remote Sensing p.6, 5th ed. (2011)

Remote sensing is… the practice of deriving information about the Earth’s land and water surfaces using images acquired from an overhead perspective, by employing electromagnetic radiation in one or more regions of the electromagnetic spectrum, reflected or emitted from the Earth’s surface. Campbell and Wynne Introduction to Remote Sensing p.6, 5th ed. (2011)

The Electromagnetic Spectrum CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=2521356

Types of Sensors Visible & Reflected IR Thermal IR Microwave Remote Sensing Thermal IR Remote Sensing Microwave Remote Sensing Radiation Source >> Object >> Type >> Sun Object Object Sensor Reflecting Radiating Radiating Reflecting Passive Passive Passive Active Spectral Radiance >> © Asian Institute of Technology, 2014, All Rights Reserved

Microwave Radiation 10GHz 1GHz 0.2μm 1.0μm 10μm 1mm 10mm 10cm 1m Visible Microwave Bands Middle infra-red Thermal infra-red Ka Ku X C S L P UV Near infra-red The electromagnetic spectrum (after NASA/JPL, 1988) 100 Transmittance (%) 50 0.2 μm 1.0μm 10μm 1mm 10nm 10cm 1m Wavelength X, C, S, L bands are used for SAR on-board satellites Characteristic of atmospheric spectral transmittance (after NASA/JPL, 1988) © Remote Sensing Technology Center of Japan, 2014, All Rights Reserved

Surface scatter (Reflection) mechanism lake grass forest ©METI/JAXA © Remote Sensing Technology Center of Japan, 2014, All Rights Reserved

Backscatter change in a paddy field Open water Planting Vegetated weak strong HH backscattering

Seasonal change Seasonal changes in microwave backscatter provide useful information to detect paddy field area. SAR Backscatter Low High

Sentinel 1A 11 Aug 2015 Innundated paddies are dark

Sentinel 1A 22 Oct 2015 After growing and/or harvest, more backscatter. The river, however, has flooded!

Asian Development Bank (ADB) MOOC

Tana River Basin, Kenya

Example case of area around Bura Irrigation Project

Sentinel 2A 22 Jan 2016 Healthy, growing vegetation is in red. If all images were this quality, the classification would be easy. The pixel size is 15m.

The problem with clouds…

Landsat 8 OLI 10 Jan 2016

Landsat 8 OLI 26 Jan 2016

Landsat 8 OLI 11 Feb 2016

Landsat 8 OLI 27 Feb 2016

Landsat 8 OLI 14 Mar 2016

Landsat 8 OLI 30 Mar 2016

Landsat 8 OLI 15 Apr 2016

Landsat 8 OLI 01 May 2016

Landsat 8 OLI 17 May 2016

Landsat 8 OLI 02 Jun 2016

Landsat 8 OLI 18 Jun 2016

Landsat 8 OLI 04 Jul 2016

Only 1 out of 11 Landsat 8 OLI images are usable for the current year! For Sentinel 2A, there are only 2 usable images…

The solution is to use active microwave sensors (SAR) that can see through clouds!

Sentinel 1A 17 Jan 2016 Healthy vegetation is bright. Resolution is nominally 10m but despeckling reduces that a bit.

Sentinel 1A 05 Mar 2016

Sentinel 1A 29 Mar 2016

Sentinel 1A 22 Apr 2016

Sentinel 1A 16 May 2016

Sentinel 1A 09 Jun 2016

Sentinel 1A 03 Jul 2016

Sentinel 1A 20 Aug 2016

Sentinel 1A 13 Sep 2016

Spatial Resolution: Landsat 8 OLI vs. Sentinel 2A vs. Sentinel 1A

Landsat 8 OLI 04 Jul 2016

Sentinel 2A 30 Jun 2016

Sentinel 1A 03 Jul 2016

A close-up of the river vegetation

Landsat 8 OLI 04 Jul 2016 Landsat is good but the 30m resolution loses to Sentinel 2A on the next slide.

Sentinel 2A 30 Jun 2016

Sentinel 1A 03 Jul 2016 Sentinel 1 is not as good as Sentinel 2 because it has much less spectral resolution, however, given the prevalence of clouds, it is a great resource.

Acquiring SAR data https://vertex.daac.asf.alaska.edu/

Processing SAR data http://step.esa.int/main/download/

For questions and/or comments, please write: ballatore@g.harvard.edu