Spring '17 EECS 725 - Intro to Radar Systems Analysis of the SMAP mission radar and possible extension to Martian soil Presented by: Shravan Kaundinya Dept. of EECS The University of Kansas 4/28/2017 Spring '17 EECS 725 - Intro to Radar Systems

Spring '17 EECS 725 - Intro to Radar Systems Outline Background – Soil Moisture Overview of SMAP Radar System Parameters Radar System Design Design Analysis Received Power computations Summary and Future Work 4/28/2017 Spring '17 EECS 725 - Intro to Radar Systems

Spring '17 EECS 725 - Intro to Radar Systems Soil Moisture Importance of soil moisture measurement [1]: Agricultural needs Water resource management Better understanding of Earth’s water, energy, and carbon cycle Monitor and predict droughts and floods Analyze the different impacts of climate change on soil moisture Factors to consider [2]: Radar – Frequency, Look/Incidence angle, Polarization (HH, VV, HV, VH) Terrain – Surface roughness, Dielectric properties, Soil constituents (sand, silt, and clay), Vegetation (height, density, and moisture) 4/28/2017 Spring '17 EECS 725 - Intro to Radar Systems

Soil Moisture Active Passive (SMAP) Satellite launched by NASA to measure surface soil moisture and freeze-thaw state Active – Synthetic Aperture Radar, Passive – Radiometer Combine data from radar (high resolution but low accuracy) and radiometer (low resolution but high accuracy) Polar, sun-synchronous orbit at an altitude of 680 km [3] Mission Timeline Launch 31 January, 2015 Reflector deployed February 2015 Science acquisition mode started April 2015 Radar stops transmitting July 2015 Initial calibration completed August 2015 Complete radar failure September 2015 End of Mission May 2018 Fig. 1. Artistic rendition of SMAP in orbit [3] 4/28/2017 Spring '17 EECS 725 - Intro to Radar Systems

SMAP SAR view of San Francisco Bay [Yueh, et al. (2015)] 4/28/2017 Spring '17 EECS 725 - Intro to Radar Systems

Radar System Parameters Operating frequencies Tunable from 1.217 to 1.275 GHz Pulse Repetition Frequency (PRF) 2.9 kHz Pulse length 15μs Transmit Bandwidth 1 MHz Peak transmit power (at output of amplifier) 500 W Front end: Rotating 6m reflector fed by a dual-polarized, horn antenna (shared by both radar and radiometer) Antenna parameters [3]: Beamwidth – 2.7o (0.05 rad) Peak gain – 36 dBi Look angle – 35.5o (0.62 rad) Incidence angle – 400 (0.7 rad) Reflector rotation rate – 13 to 14.6 rpm Total (overlapping) swath width – 1000 km Real aperture resolution – 30 km [High radar resolution (3 km) & low accuracy] + [Low radiometer resolution (40 km) & high accuracy] = Intermediate resolution (10 km) and accuracy Fig. 2. Rendition of the conically scanning antenna beam mapping a swath on the surface [3] 4/28/2017 Spring '17 EECS 725 - Intro to Radar Systems

Radar system design Fig. 3. Simplified block diagram of the SMAP radar [3] Fig. 4. Time-domain representation of transmit and echo signals [3] 4/28/2017 Spring '17 EECS 725 - Intro to Radar Systems

Spring '17 EECS 725 - Intro to Radar Systems Design Analysis Cross-track resolution reported: “approximately 250 m” [5] Using Bandwidth (1 MHz) and Incident angle, resolution obtained is 233.35 m Calculated blind range = 2.25 km (using pulse length of 15μs) Pulse Repetition Frequency (PRF) used: 2.9 kHz [3] Using orbital velocity (7.5 kms-1) for an altitude of 680 km and diameter of antenna (6 m), minimum PRF obtained is 2.5 kHz Using pulse duration and total propagation time of wave for both slant range lengths, maximum PRF obtained is 6.3 kHz 4/28/2017 Spring '17 EECS 725 - Intro to Radar Systems

Received Power using Radar Equation Soil moisture is derived from the backscattering coefficient depending on the received power To investigate possible received power range, backscattering coefficient is approximated Scattering coefficient for soil at frequency of 1.1 GHz (SMAP 1.2 GHz) and incidence angle of 30 degrees (SMAP 40 degrees) is used [6] Received Powers: Low moisture & low roughness = -102 dBm Low moisture & high roughness = -82 dBm High moisture & low roughness = -98 dBm High moisture & high roughness = -76 dBm If a 12-bit A/D converter is used and has a dynamic range of +10 to -65 dB, then required receiver gain to boost worst case received power is 40 dB (approx.) Fig. 5. Soil with low levels of moisture content [6] Fig. 6. Soil with high levels of moisture content [6] 4/28/2017 Spring '17 EECS 725 - Intro to Radar Systems

Summary and Future work Unique method of combining active (radar) and passive (radiometer) systems to obtain soil moisture Design parameters like cross-track range resolution and PRF have been verified Possible received power range is calculated based on approximate soil backscattering coefficients Other parameters like noise power and hence SNR could be calculated based on reasonable assumptions (noise figure) Analysis of data processing method (SAR) Investigation and analysis of Martian Soil Possible extension of soil moisture measurement on Mars 4/28/2017 Spring '17 EECS 725 - Intro to Radar Systems

Spring '17 EECS 725 - Intro to Radar Systems References Northon, Karen. "NASA Launches Groundbreaking Soil Moisture Mapping Satellite." NASA. NASA, 19 Mar. 2015. Web. 27 Apr. 2017. Ulaby, F. "Radar measurement of soil moisture content." IEEE Transactions on antennas and propagation 22, no. 2 (1974): 257-265. Entekhabi, Dara, Simon Yueh, Peggy E. O’Neill, Kent H. Kellogg, Angela Allen, Rajat Bindlish, Molly Brown et al. "SMAP Handbook–Soil Moisture Active Passive: Mapping Soil Moisture and Freeze/Thaw From Space." (2014). Yueh, Simon, Kent Kellogg, Peggy O'Neill, and Eni Njoku. Early Results from NASA Soil Moisture Active Passive Mission. 2015. Accessed April 27, 2017. Keyword: NASA SMAP. Spencer, Michael, Kevin Wheeler, Chris White, Richard West, Jeffrey Piepmeier, Derek Hudson, and James Medeiros. "The Soil Moisture Active Passive (SMAP) mission L-band radar/radiometer instrument." In Geoscience and Remote Sensing Symposium (IGARSS), 2010 IEEE International, pp. 3240-3243. IEEE, 2010. Ulaby, Fawwaz T., Percy P. Batlivala, and Myron C. Dobson. "Microwave backscatter dependence on surface roughness, soil moisture, and soil texture: Part I-bare soil." IEEE Transactions on Geoscience Electronics 16, no. 4 (1978): 286-295. 4/28/2017 Spring '17 EECS 725 - Intro to Radar Systems