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Progress	Report:	 Subsidence	in	the	Central	Valley,	California

Tom	G	Farr,	Cathleen	Jones,	Zhen	Liu

Jet	Propulsion	Laboratory	

California	Institute	of	Technology

Executive	summary

Subsidence	caused	by	groundwater	pumping	in	the	Central	Valley	has	been	a	problem	for	

decades.	Over	the	last	few	years,	interferometric	synthetic	aperture	radar	(InSAR)	has	been	

used	from	satellites	and	aircraft	to	produce	maps	of subsidence	with	sensitivity of	fractions	

of	an	inch.	For	this	study,	we	have	obtained	and	analyzed	Japanese	PALSAR	data	for	2006	-

2010	and	Canadian	Radarsat-2	data	for	the	period	May	2014	– January 2015	and	produced	

maps	of	the	total	subsidence for those periods.	As	multiple	scenes	were	acquired	during	

these periods,	we	can	also	produce	time	histories of	subsidence	at	selected locations	and	

transects	showing	how	subsidence	varies	both	spatially and	temporally.	Geographic	

Information	System	(GIS)	files	will	be	furnished	to	DWR	for	further	analysis	of	the	4	

dimensional	subsidence	time-series	maps.	

For both periods,	two already known	main	subsidence	bowls	in	the	San	Joaquin	Valley	have	

been	mapped: The	larger	is	centered	on	Corcoran	and	extends 60	miles	to	the	NW,	affecting	

the	California	Aqueduct.	For	the	period	2006	- 2010,	maximum	total	subsidence	was	found	

to	be	about	37”	near	Corcoran.	From	May	2014	– January	2015,	maximum	subsidence	of	

over	13” was	found just	SE	of	Corcoran.	A second	bowl	is	centered	on	El	Nido and	is	

approximately	25	miles	in	diameter,	encompassing most	of	the	East	Side	Bypass.	From	

2006	- 2010	maximum	subsidence	totaled	about	24”	S	of	El	Nido.	From	May	2014	– January	

2015,	maximum	subsidence	of	about	10” occurred	in	the	same	area.	In	the	Sacramento	

Valley,	a	single	area	N	of	Yolo	subsided about	6”	from	2006	- 2010.	From	May	to	November	

2014,	an	extended area	W of	Yolo	showed	small	areas	with	a	maximum	subsidence	of	about	

3”;	another	diffuse	area	N	of	Yolo	had	a	maximum	subsidence	of	about	2.5”;	and	an	

unusually	small	intense	area	of	subsidence	just	W	of	Arbuckle	showed	a	maximum

subsidence	of	about 5”.

InSAR data	were	also	collected	by	the	NASA	UAVSAR	airborne	platform	over	two	swaths	

centered	on	the	California	Aqueduct	to	evaluate	subsidence	on	or	near	the	aqueduct using	a	

high	spatial	resolution	instrument.	The	first	swath	covered the	California	Aqueduct	from	

San	Luis	Reservoir	to	Kettleman	City,	and	the	second	from	due	west	of	Buttonwillow	to	the	

Edmonston	Pumping	Plant. Time	series	analysis	showed	subsidence	to	be	highly	variable	

across	this	extent	and	to	have	increased	sharply	starting	in	summer	2014.	Impact	on the	

Aqueduct	from	groundwater	withdrawal	is	greater	in	the	northern	swath. The	greatest

subsidence	directly	impacting	the	California	Aqueduct	was	observed	between	Huron	and	

Kettleman	City,	where	a	subsidence	bowl	of depth	about	14”	was	centered	less	than	half	a	

mile	from	the	Aqueduct.	The	subsidence	bowl	extended	beyond	the	aqueduct	and	caused	

>8”	of	subsidence	along	a	1.3	mile	stretch	of	the	aqueduct,	with	a	maximum	of	about	13”	

subsidence.	We	note	that	subsidence	values	measured	with	UAVSAR	InSAR	are	averaged	

across	a	pixel	of	 area	> 20’	x	20’, so	maximum	values	measured	on	the	ground	could	be	

higher	at	locations	within	the	pixel.	
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Introduction

The	problem	of	subsidence

The	aquifer	system	of	the	southern	Central Valley	has	both	unconfined	and	confined	parts	

caused	by	alternating	layers	of	coarse	and	fine-grained	sediments.	Water	in	the	coarsegrained,	unconfined	or	water-table	aquifers	can	be	extracted	or	recharged	easily	and	

causes	only	minor	‘elastic’	compaction	reflected	as	seasonal	subsidence	and	rebound	of	

water	levels	and	the	land	surface.	Most	water	wells	exploit	the	deeper	confined	aquifers,	

and	withdrawal	of	water	from	them	causes	drainage	of	the	fine-grained	confining	layers	

called	aquitards.	Significant water	is	available	in	the	aquitards.	These,	however, drain	

slowly	and	compact	both	elastically	as	well	as	inelastically.	In	general,	if	water	levels	are	

not	drawn	too	low,	when	pumping	ceases	water	recharges	the	aquitards	and	their	

structure	expands.	However,	if	water	levels	are	drawn	too	low,	then	an	irreversible	

compaction	of	the	fine-grained	aquitards	occurs.	The	water	cannot	recharge	the	layers,	

causing	permanent	subsidence and loss	of	some	groundwater	storage	capacity (see	

Galloway	et	al.,	1999	pages	8-13;	Bertholdi	et	al.,	1991	for	reviews).

Measuring	and	understanding	subsidence	as	a	function	of	groundwater	dynamics	will	

greatly	improve	management	of	that	important	resource,	and	in	addition	the	effect	of	

subsidence	on	infrastructure	can	also	be	monitored using	InSAR.	Roads	can	be	broken	by	

fissures,	pipelines	have	been	exhumed,	and	the	slope	of	the	land	can	be	altered,	changing	

drainage	patterns.	This	last	effect	has	proven	to	be	a	significant	problem	on	the	California	

Aqueduct,	where	the	canal	lining	has	been	raised	in	multiple	locations	over	the	years in

order	to	preserve	flow.	Areas	of	low	relief	that	have	subsided	are	also	subject	to	flooding.	

How	InSAR	works

Key	points:	

1) InSAR	measures	subsidence	relative	to	a	stable	location	chosen	during	processing.	

2) InSAR	measures	subsidence	relative	to	the	first	image	date	in	a	series.	

3) Radar	measurements from	multiple	satellites	can	not	be	combined

interferometrically.	

4) However,	subsidence	measurements may	be	combined	if	they	overlap	in	time.	

Interferometric	synthetic	aperture	radar	(InSAR) is	a	technique	whereby	surface	change	

occurring	between	two	radar	imaging	passes	may	be	measured	and	mapped	to	high	

precision (see	Madsen	and	Zebker,	1998;	Massonnet,	1997 for	reviews).	The	ability	to	map	

surface	deformation	of	a	fraction	of	an	inch over	large	areas	at	spatial	resolutions	of	100	

feet	or	so has	opened	up	new	possibilities	for	remote	monitoring	of	groundwater	

resources.	Most	applications	have	used	satellite	radar	systems, although	airborne	systems	

are	also	available.	

The	technique	works	by	acquiring	images	from	the	same	viewing	geometry	at	two	different	

times	between	which	a	change in	the	surface	position has	occurred.	The	phases	of	the	

returning	radar	waves	from	the	two	acquisitions	are	subtracted	to	create	a	phasedifference	map,	or	interferogram, that	can	be	processed	to	create	a	map	of	changes	in	
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distance	along	the	line-of-sight direction that	are precise	to	fractions	of	the	radar	

wavelength (typical	wavelengths	are	1-10	inches).	There are	however	some	noise	factors	

which	must	be	considered:	orbital	error,	atmospheric	noise,	topography	error and	phase	

decorrelation	error.	Orbital	and	topography	errors	are	largely	handled	in	the InSAR	data	

processing.	Atmospheric	water	vapor	and	other	variations	in	Earth’s	troposphere	can	

introduce	phase	delay	artifacts	that	mimic	surface	changes.	This	is	usually	dealt	with	by	

analyzing	many	interferometric	pairs	and	averaging	(stacking)	assuming ground	

deformation	is	steady and	atmospheric	phase	is	random	in	time.	For	time-varying	

deformation	signals,	more	sophisticated	spatiotemporal	filtering	can	be	applied	during	

InSAR	time	series	analysis	to	mitigate	the	effects	of	atmospheric noise	(e.g.,	Galloway	et	al.,	

1998;	Lanari	et	al.,	2004;	Ozawa	and	Ueda,	2011;	Chaussard	et	al.,	2013). Another	problem,	

especially	acute	in	agricultural	areas	like	the	Central	Valley,	is	small-scale	surface	changes	

near	the	scale	of	the	radar	wavelength.	Crops	blowing	in	the	wind	or	fields	plowed	between	

radar	image	acquisitions can	spoil	the	phase	coherence	between	the	two	radar	images	and	

cause	loss	of	information.	This	effect	can	be	ameliorated	by	using	a	longer	wavelength	and	

selecting	interferometric	pairs	that	have	small	orbital	baseline	separations	and	temporal

differences.	

After	many	pairs	of	radar	images	over	an	area	have	been	processed	into	interferograms,	

they	can	be	further	analyzed	to	create	a	time	series	of	surface	deformation.	This	is	done	by	

an	InSAR	time	series	inversion	algorithm	called	the	Small	Baseline	Subset	(SBAS)	method	

(e.g.,	Berardino	et	al.,	2002;	Sansosti	et	al.,	2010).	SBAS makes	use	of interferometric	pairs	

that	have	small	spatial	baselines	and	short	temporal	separations.	The	time	series	is	

constructed	pixel	by	pixel	and	requires	no	assumptions	on	the	continuity	or	stability	of	

phase	in	time.	Proper	choice	of	the	reference	location is needed	in	order	to	tie	together	the	

relative	InSAR	measurements	into a	consistent reference	frame.	The	reference	location	(or	

pixel)	is	usually	chosen	at	a	place	that	is	stable	compared	to	the	deformation	of	interest	

based	on	in situ geodetic	measurements	or	a	priori information.

The	InSAR	time	series	analysis	produces	a	history	of	line-of-sight	(LOS)	surface	

displacements	similar	to	GPS	time	series	observations but	with	much	higher	spatial	

resolution.	Unlike	stacking,	which	has	no	temporal	resolution,	InSAR	time	series	recover	

both	long-term	mean	velocities,	and	time	varying	components,	while	at	the	same	time	

isolating	atmospheric	delays	(as	well	as	surface	deformation)	into	the	respective	SAR	

image	epochs	(e.g.,	Lanari	et	al.,	2004).	This	technique	has	been	applied	successfully	for	

imaging	non-steady-state	deformation	at	volcanoes	(Lundgren	et	al.,	2004), deforming	

plate	boundaries	(Lundgren	et	al.,	2009),	and	aquifer	dynamics	(Farr	and	Liu,	2015;	Farr,	

2011;	Lanari	et	al.,	2004).	After	the	initial	time	series	inversion,	temporal	and	spatial	

filtering	can	be	applied	to	further	suppress	atmospheric	noise	and	smooth	the	deformation	

time	series.	Since	atmospheric	noise	is	spatially	correlated	but	temporally	uncorrelated,	its	

net	effect	on	the	InSAR	time	series is	negligible.	The	estimated	measurement	precision for	

InSAR	time	series	is	generally	a	small	fraction of	a	wavelength,	depending on	the	InSAR	

acquisitions	and	noise	levels	(e.g.,	Galloway	et	al.,	1998;	Ozawa	and	Ueda,	2011;	Chaussard	

et	al.,	2013). In	the	case	of	the	Radarsat-2	measurements	shown	later,	uncertainties

associated	with	the	vertical	displacement	(subsidence/uplift)	measurements	were	

determined	to	be	less	than	1”	and	usually	less	than	0.5”.		These	uncertainties	cover	random	
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errors,	but	do	not	include	systematic	errors	related	to	choice	of	reference	location	or	

unwrapping	errors.	

A	final	step	in	post-processing is	to	use	the	assumption that	subsidence	is	mainly	in	the	

vertical	direction,	so	the	line-of-sight	measurement from	the	radars	can	be	projected	to	the	

vertical.	This	allows	measurements from	multiple	satellites	to	be	compared with	each	other	

and	with	GPS	and	traditional	surveying	data.	

Several	groups have	made	studies	of	the	effects	of	groundwater	withdrawal	and	recharge	

on	InSAR	measurements	of	deformation	of	the	Earth’s	surface (e.g.	Reeves	et	al.,	2011;	

Calderhead	et	al.,	2011;	Lu	and	Danskin,	2001;	Amelung	et	al.,	1999).	Preliminary	

evaluations	of	InSAR	applications	to	groundwater	monitoring	have	been	made over	the	last	

few	years in	Los	Angeles	(Bawden	et	al.,	2001),	the	Antelope	Valley	(Galloway	et	al.,	1998),	

Las	Vegas	(Hoffmann	et	al.,	2001;	Bell	et	al.,	2008),	the	Santa	Clara	Valley	(Sneed	et	al.,	

2003),	the	Coachella	Valley	(Sneed	and	Brandt,	2007),	and the	southern	Central	Valley	

(Farr	and	Liu,	2015;	Farr,	2011;	Sneed	et	al.,	2013;	Borchers and	Carpenter,	2014).	

A	number	of	satellite	systems	have	been	flown	over	the	years	to	provide	InSAR	data	(Table	

1).	Note	that	while	the	satellites	span	only	a	few	years	each,	they	overlap	in	time	allowing	

their time	series	to	be	compared.	That	is	a	focus	of	ongoing	research	in	our	group at	JPL.	

For	this	report,	PALSAR	images	spanning	the	period	June	2007	– December	2010	and	

Radarsat-2	images for	the	period	May	2014	– January	2015 were	processed	to	two	

independent	time	series.	Details of	the	data	used	are	listed	in	the	Appendix.	Further	work	

under	this	task will	fill	the	gap	between	the	PALSAR	and	Radarsat-2	results	using	Radarsat1	data.	

Table	1.	Past,	present,	and	future	radar	satellites.
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UAVSAR,	which	is	an	L-band	SAR	flown	on	a	G-3	aircraft, has	a	much	higher	signal-to-noise	

ratio	than	satellite	SARs,	usually	achieving	a	factor	of	100	increase	in	signal	through	the	use	

of	a	high-power	instrument	transmitting	from	41,000	ft. altitude	rather	than	from	Earth	

orbit. It	also	has	higher	spatial	resolution	than	the	satellite	SARs,	with	<6’ single-look	

resolution,	which	allows	higher	resolution	following	spatial	averaging	to	reduce	the	phase	

noise. The	reduction	in	phase	noise	means	that	deformation	measurement	accuracy	is	

increased	and temporal	decorrelation	is	reduced.	The	practical	outcome	is	that	a	larger	

proportion	of	a	UAVSAR	scene will	produce	useful	measurements. Previous	InSAR	results	

from	UAVSAR	include	measurements	of	fault	slip	in	California	(Donnellan	et	al.,	2014),	

landslides	along	the	San	Andreas	fault	(Scheingross	et	al.,	2013),	and	sinkhole	precursory	

ground	movement	in	Louisiana	(Jones	and	Blom,	2014).

UAVSAR data	processing	followed similar	steps	to	those	used	for	the	satellite	data. We	

eliminated	very	low	coherence	areas	from	the	analysis	by	masking	out	pixels	with	average	

coherence	less	than	0.285	or	with	coherence	<	0.60	in	all	interferograms. The	average	is	

taken	over	the	interferometric	coherence	associated	with	each	interferogram	in	the	stack.

This	masking	step	eliminated	most	open	water	and	land	areas	that	experienced	high	and	

persistent	temporal	decorrelation. A	temporal	filter	of	width	1	month was	applied	to	

smooth	the	results;	this	value	was	chosen	to	be	sufficiently	short	that	we	are	able	to	resolve	

when	subsidence	rates	changed	during	2014. Pixels	were	classified	based	upon	their	

average	coherence, and	adaptive	spatial	filtering	was	applied such	that low	coherence	

areas	were	averaged	with	nearby	same-class	pixels	to	reduce	noise, and	high	coherence	

pixels were not	averaged	at	all. Uncertainties	in	the	derived	subsidence	values	were	

obtained	through	a Jacknife	resampling procedure	whereby	the	SBAS	processing	was	run	

on	the	stack	with	data	from	a	single	acquisition	removed,	repeated	with	removal	of	each	

acquisition	date	in	the	series. This	procedure	estimates	the	combined	effect	of	random	

errors	and	systematic	errors	associated	with	a	single	acquisition. The	uncertainties	in	the	

cumulative	subsidence	derived	from	UAVSAR	InSAR	are in	the	range	of 0.25”	to	1.0” across	

most	of	the	imaged	area. Estimates	for	each	pixel	are	included	in	the	GIS	products

provided to	DWR,	and	shown	in	plots	in	an	appendix	to	this	document.	

The	UAVSAR	data	analysis	methods	used	in	this	work	are	based	on	procedures	developed	

to	monitor	the	levees	in	the	Sacramento-San	Joaquin	Delta	using	the	instrument	(Jones	et	

al.,	2011;	2012;	2015). Unlike	in	the	Central	Valley,	groundwater	pumping	is	not	a	problem	

in	the	Sacramento-San	Joaquin	Delta. However,	subsidence	from	aerobic	oxidation	of	the	

soil	and	compaction	of	the	soil	from	pumping	to	remove	water	from	the	upper	layers	of	the	

soil	is	common	throughout	the	area	(Deverel	and	Leighton,	2010).

San	Joaquin	Valley Subsidence

Maps	of	subsidence	in the	San	Joaquin	Valley were	made for	the	period	June	2007	–

December	2010 (Fig.	1;	PALSAR)	and	May	2014	– January	2015	(Fig.	2;	Radarsat-2).	Two	

main	subsidence	bowls	can	be	seen	in	the	maps of	total	subsidence:	 one	in	the	Tulare	basin

centered on	Corcoran and	one	S	of the	town	of	El	Nido.	The	maximum	total	subsidence for	

the	earlier period in	the	Tulare	Basin was	over 37”	near	Corcoran.	The	maximum	

subsidence	S	of El	Nido	was	approximately	24”.	During	the	more	recent	period,	we	see	that,	

while	the	two	bowls	are	generally	similar,	some	of	the	details	have	changed.	The	largest	
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subsidence	S	of	Corcoran	totals	over	13” while	another	diffuse	area	is	located	NW	of	

Corcoran	with	a	subsidence	of	up	to	9”.	Subsidence	of	over	3”	extends	W	to	the	California	

Aqueduct.	This	southern	subsidence	bowl	is	about	60	x	25	miles.	The	other	main	

subsidence	bowl	S	of	El	Nido	subsided	about	5-6”	with	pockets	up	to	10”.	The	East	Side	

Bypass	runs	right	through	the	main	part	of	the	subsidence	in	this	area.	

Figure	1.	Total	subsidence	in	the	San	Joaquin	Valley	for	the	period	June	2007	– December	2010	as	

measured	by	the	Japanese	PALSAR	and	processed	at	JPL.	Two	large	subsidence	bowls	are	evident	

centered	on	Corcoran	and	S	of	El	Nido.	Note	the	narrow	banana-shaped	subsidence	feature	at	

bottom	center.	That	corresponds	to	the	Belridge	Oil	Field,	which	is	subsiding	due	to	oil	extraction

(Fielding	et	al.,	1998).		An	animation	of	the	subsidence	in	the	Tulare	basin	can	be	seen	at:	

http://photojournal.jpl.nasa.gov/catalog/PIA16293.
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Figure	2.	Total	subsidence	in	the	San	Joaquin	Valley	for	the	period	3	May	2014	– 22	January	2015 as	

measured	by	the	Canadian	Radarsat-2 and	processed	at	JPL.	The	same	two	large	subsidence	bowls	

visible	in	Figure	1	at Corcoran	and	El	Nido are	clearly	visible.	A preliminary	version	of	this	map was	

presented	as	Figure	15	in	the	recent	Public	Update	for	Drought	Response	(CDWR,	2014).	
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Figure	3.	Subsidence	histories	of	a	few	locations	in	the	San	Joaquin	and	Sacramento	Valleys.	Top:	

2006	– 2010	(PALSAR);	Bottom:	May	2014	– Jan.	2015	(Radarsat-2).	Corcoran	max	is	located	in	the	

maximum	subsidence	pocket	just	N	of	Corcoran.	El	Nido	max	is	located	in	the	pocket	just	S	of	El	

Nido.	Arbuckle	is	located	just	W	of	the	town	of	Arbuckle	in	the	Sacramento	Valley	and	Yolo	is	at	the	

center	of	the	subsidence	feature	N	of	Yolo	(Fig.	5).	

The	deformation	histories	of	a	few	selected	locations	in	the	San	Joaquin Valley	are	plotted	

in	Figure	3.	The	large	maximum	subsidence	in	the	Corcoran	area	is	clear	and	shows	

virtually	no	recovery	at	any	time	in	either	period	of	measurement,	although	the	rate	seems	

to	decrease	in	2010.	Likewise,	the	maximum	subsidence	location	near	El	Nido	shows	little	

seasonal	change	except	for	some	flattening	in	2010	and	January 2015.	The	histories	for	

Arbuckle	and	Yolo	are	discussed	later	in	the	Sacramento	Valley	section.	
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Figure	4.	Transects	showing	total	subsidence	in	the	vicinity of	the	California	Aqueduct	and	the	East	

Side	Bypass.	The	transects	extend	from	N	to	S	with	the	end	points	located	where	the	canals	

intersect	the	radar	images.	Top:		Total	subsidence	from	June	2007	– December	2010 (PALSAR).	

Note	the	deep	subsidence	pit	about	midway	along	the	East	Side	Bypass.	That	corresponds	to	the	

orange	area	on	the	map	(Fig.	1).		Bottom:		total	subsidence	from	3	May	2014	– 22	January	2015

(Radarsat-2).	Note	the	deep	subsidence	pit	about	midway	along	the	East	Side	Bypass.	That	

corresponds to	the	orange	and	red	area	on	the	map	(Fig.	2).	The	two	sharp	pits	between	miles	75	

and	80	on	the	California	Aqueduct	correspond	to	the	features	observed	by	UAVSAR	(Fig.	12).	

The	transects	shown	in	Figure	4 give	a	more	detailed	picture	of	the	total	subsidence	

measured	in	the	vicinity	of	the	California	Aqueduct	and	the	East	Side	Bypass over	the	two	

periods	of	measurement.	It	is	clear	that	the	East	Side	Bypass	has	suffered	much	more	

subsidence,	concentrated	in its central	area.	In	contrast,	areas	in	the	vicinity	of	the	

California	Aqueduct	experienced	up	to 5”	of	subsidence in	2006	- 2010,	and	a	similar	

amount	in	the	May	2014	– January	2015	time	period.	These	amounts	correspond	to	

averages	over	the	processed	pixel,	not	the	values	on	the	aqueduct	structure	itself.	
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One	new	concentrated	zone	along	the	California Aqueduct	stands	out	in	Figure	4,	between	

75	and	80	miles.	This	subsidence	area	appears	to	be	a	new	zone,	and	was detected	at	

higher	spatial	resolution by	UAVSAR,	as discussed	later in	this	report.

Sacramento	Valley	Subsidence	

Subsidence maps for	the	southern part	of	the	Sacramento	Valley were	also	produced	for	

this	report, covering	the	period	December	2006	to	May	2010 (PALSAR;	Fig.	5)	and	20	May	

2014	to	28	November	2014	(Radarsat-2;	Fig.	6). Only	one area	of	significant	subsidence	

was	detected	and	mapped in	the	earlier	period:	just	N	of	Yolo	a	bowl	about	7	miles	across	

had	a	maximum	subsidence	of	about	6”.	This	matches	well	with	subsidence	mapped	by	GPS	

survey from	1999	- 2005	and	reported	in	D’Onofrio	and	Frame	(2006).

Figure	5.	Total	subsidence	in	the	Sacramento Valley	for	the	period Dec.	2006	- May 2010	as	

measured	by	the	Japanese	PALSAR	and	processed	at	JPL. One	subsidence	bowl	is	shown	north	of	

Yolo.	

The	Radarsat-2	map (Fig.	6) shows	3	areas	of	significant	subsidence between	20	May	2014	

to	28	November	2014:	an	extended	area	W	of	Yolo includes	small	areas	with	a	maximum	

subsidence	of	about	3”;	another	diffuse	area	N	of	Yolo	had	a	maximum	subsidence	of	about	

2.5”;	and	an	unusually	small	heavily	subsiding	area	just	W	of	Arbuckle	showed	a	maximum	

subsidence	of	about 5”.
11

Figure	6.	Total	subsidence	in	the	Sacramento Valley	for	the	period	20 May	2014	– 28	November	

2014 as	measured	by	the	Canadian	Radarsat-2 and	processed	at	JPL. Two	diffuse	subsidence	areas	

can	be	seen	west	and	north	of	Yolo	and	a	small,	deep	subsidence	bowl	is	evident	just	west	of	

Arbuckle.	

Subsidence	histories	of	two	locations	in	the	Sacramento	Valley	are	shown	in	Figure	3.	The	

area	of	maximum	subsidence	in	the	PALSAR	data	north	of	Yolo	(Fig.	5)	totals	about	6”	over	

the	earlier	3.5	year	period	and	about	2”	in	the	last	half	of	2014.	The	small	area	of	intense	

subsidence	evident	near	Arbuckle	in	2014	(Fig. 6) shows	an	uneven	subsidence	with	time

in	Figure	3,	totaling	about	5”	for	the	last	half	of	2014,	but	no	subsidence	in	2006	- 2010.	

UAVSAR	Results Along	California	Aqueduct

Figure	7 shows	the	areas	in	the	Central	Valley	covered	by	the	two	UAVSAR	flight	lines, and	

the	measured	subsidence	in	both	imaged	areas. The	swath to	the	north	showed	locations	

experiencing	significantly	greater	subsidence	than	was	observed	in	the	southern	swath.

Figure 8 shows	only	the	northern	imaged	swath.	In	this	stretch	of	the	aqueduct	there	is	an	

extended	region	of	subsidence	in	the	center,	an	area	of	very	high	subsidence	with	a	very	

well-defined	locus	to	the	south,	and	several	other	areas	showing	subsidence	of	3”-5”. These

areas	are	shown	in	more	detail	in	Figures	9-11,	where	time	histories	of	individual	points	

made	clear	that	even	though	the	northern	swath	(line	14511)	was	imaged	for	a	longer	
12

period	of	time	than	the	southern	swath	(line	13300),	this	is	not	the	reason	why	higher	

cumulative	subsidence	was	measured	there.	

Figure	7.	Overview	of	area	in	the	Central	Valley	imaged	with	UAVSAR,	showing	the	broad	patterns	

of	subsidence	observed. The	areas	of	significant	subsidence	encompassing	the	aqueduct	during	the	

imaged	time	period	occur	entirely	in	the	northern	section	.These	swaths	were	planned	to	well	

image	the	California	Aqueduct,	and	therefore	miss	the	large	subsidence	bowls	to	the	east	that	were	

seen	in	the	satellite	SAR	results.		The	swath	to	the	north	is	UAVSAR	line	14511	and	shows	

cumulative	subsidence	between	19	July	2013	and	10	March	2015.	The	swath	to	the	south	is	

UAVSAR	line	13300	and	shows	cumulative	subsidence	between	2	April	2014	and	7	January	2015.

The	stars	indicate	the	reference	points	used for	each	line,	which	are the	locations	in	each	swath

taken	to	have	experienced	no	subsidence	and	against	which	other	locations	are	compared.
13

Figure	8.	Cumulative	subsidence	between	July	2013	and	March	2015	measured	with	UAVSAR	in	the	

Central	Valley	between	San	Luis	Reservoir	and	just	south	of	Check 21. A	new	locus	of	subsidence,	

which had	the largest	aqueduct	impact,	occurred	near	Check	20	(see	Fig.	9). From	south	of	Check	15	

to	Check	17	is	an	area	that	has	historically	shown	large	subsidence	of	the	aqueduct (see	Fig.	10).		

Near	Huron	(Check	19)	is	another	area	of	subsidence,	this	one	less	extensive	in	length	(see	Fig.	11).	
14

Figure	9.	(A)	Overview of the	cumulative	subsidence	across	an	extended	area	east	of	Interstate	5,	

near	Check	20	(MP	164.69)	at	the	southern	end	of swath	14511	(Fig. 8).		Several	round,	localized	

features	are	seen in	this	section,	but	the	one	closest	to	the	aqueduct	experienced	the	most	

subsidence of	any	area	in	the two UAVSAR	swaths. (B) Enlargement showing	the	subsidence	bowl	

just	north	of	Avenal	Cut-off	Road,	with	a	well	localized	center	and	extended	impact	to	the	

surrounding	area,	including	the	aqueduct.		Limits	are placed	on	the	subsidence	overlay	layer	to	

indicate	areas	that	experienced	more	than	8”	of	subsidence	between	July	2013	and	March	2015.		

Values	represent	an	average	over	the	smoothed	pixels,	not	the	maximum	subsidence	within	each	

pixel.	(C)	Close-up of	the	section	of	the	aqueduct	nearest	the	center	of	the	bowl.		The	star	marks	the	

location	for	which	the	time	history of	subsidence	is	plotted	in	D.	(D)	Cumulative	subsidence	vs.	time

from	July	2013	(zero)	to	March	2015	(12.5”).		This	area	experienced	a	dramatic	increase	in	

subsidence starting	in	summer	2014, which	slowed abruptly	in	October	2014.
15

The	greatest subsidence	directly	impacting	the	California	Aqueduct	was	observed	

immediately	north	of	the	intersection	of	the	aqueduct	with	Avenal	Cutoff	Rd.,	between	

Huron	and	Kettleman	City,	just	north	of	Check	20	(MP164.69). At	this	location,	a	

subsidence	bowl	centered	less than	half	a	mile	from	the	aqueduct formed	during	the	study	

period. Figure	9A shows	the	subsidence	in	the	vicinity	of	this	location,	showing	at	least	

three	similar	features	that	appear	to	be	associated	with	wells. Figure	9B shows	the	locus	of	

the	subsidence	bowl	north	of	Avenal	Cutoff	Rd.	Limits	are	placed	to	indicate	the	area	that	

experienced	>8”	of	subsidence. The	main	subsidence	bowl	impacted	the	aqueduct	

significantly,	extending	from	its	center	in	an	adjacent	field	to	west	of	the	structure,	and	

caused	>8”	of	subsidence	along	a	1.3	mile	stretch	of	the	aqueduct.		In	addition,	 nearly	0.5	

miles experienced	>11”	subsidence (Fig.	9C). Figure 9D shows	the	temporal	development	

of	the	subsidence,	indicating	that	high	subsidence	in	this	area	started	around June	2015.

The	eastern	edge	of	the	aqueduct	closest	to	the	center	of	the	bowl	experienced up	to	12.5”	

of	subsidence. The	bulk	of	the	subsidence	(8”)	occurred	very	rapidly,	over	the	period	

between	June	and	October	2014.		There	is	an	indication	of	increasing	subsidence	prior	to

that time,	around	Feb.	2014,	but	at	a	much	lower rate	than	experienced	later	in	the	year.	

The subsidence	 rate	decreased by	November	2014.		More	acquisitions	are	needed	to	

determine	whether	the	rate	is	increasing	again	in	March	2015. Comparison	with results	

from	Radarsat-2	(Fig.	2,	4)	show	a	larger	amount	of	subsidence	measured	by	UAVSAR,	even	

accounting	for	the	longer	time	interval	covered	by	the	UAVSAR	data.	This	is	likely	caused	

by	the	larger	pixel	size	used	in	the	satellite	processing	(300’	vs.	25’)	and	a	slightly	longer	

temporal	filter (2	mo.	vs.	1	mo.).	

Figure	10 shows	the	cumulative	subsidence	between	Check	16	(MP122.07)	and	Check	17	

(MP132.95)	of	the	California	Aqueduct,	near	Cantua	Creek.	Although	subsidence in	this	

area	was less	(only	up	to	8”),	a	longer	stretch	of	the	aqueduct	was	affected.	Similar	to	the	

Avenal	subsidence	bowl,	the	subsidence	rate	appears	to	have	increased	dramatically	in	

spring	2014,	and	to	have	lessened	in	autumn	2014.		Figure	11 shows	the	area	immediately	

east	of	Huron,	in	the	vicinity	of	Check	19	(MP155.64).	Unlike	the	other	two	areas,	

subsidence	here	has	been	more	consistent,	albeit	with	a	noticeable	but	less	precipitous		

increase	in	rate	in	spring/summer	2014.	Here	the	cumulative	subsidence	was	about	7”	

during	the	20	months	that	the	area	was	monitored.
16

Figure	10.	(A)	Subsidence	in	the	Cantua	Creek	area,	showing	an	extended	section	of	the	California	

Aqueduct encompassing	Checks	16	and	17	that	 experienced as	much	as	8”	of	subsidence	between	

July	2013	and	March	2015. The	time	series shows that	in	this	area	there	is	seasonal	

uplift/subsidence	and	that	the	subsidence	accelerated	in	spring	2014	and	tapered	off in	fall 2014.
17

Figure	11.	 Location	immediately	east	of	Huron	where	a	short	stretch	of	the	California	Aqueduct	has	

experienced	nearly	steady	subsidence	since	July	2013,	accumulating	about	7”	of	vertical	

displacement between	July	2013	and March	2015.		There	is	larger	uncertainty	at	the	last	two	time	

steps,	which	can	be	decreased	with	additional	UAVSAR	acquisitions.

Figure	12 shows	subsidence	in	the	southern	swath,	where	only	one	area	indicated	

particularly	anomalous subsidence	directly	affecting	the	California	Aqueduct. This	is	near

where	Old	River	Rd.	crosses	the	aqueduct,	between	Check	33	(MP267.36)	and	Check	34	

(MP271.27) (Figure	13). For	this	line,	we	have	no	data	prior	to	April	2014	so	we	cannot	tell	

whether	this	is	an	area	showing	persistent	or	recent subsidence. We	do	observe	subsidence	

in	the	south-central	part	of	the	imaged	swath (Fig.	13A),	but	it	did	not	directly	affect	the	

aqueduct	during	April	2014	– Jan.	2015.		No	substantial	subsidence	is	seen	west	of	

Buttonwillow,	although	ground	subsidence	associated	with	oil extraction	is	apparent	(Fig.	

13C).
18

Figure	12.	(Top)	Cumulative	subsidence	between	April	2014	and	January	2015	measured	with	

UAVSAR	in	the	Central	Valley	between	Buttonwillow	and	the	Edmonston	Pumping	Station. The	

subsidence	is	much	less	in	this	area	than	in	the	area	to	the	north	shown	in	Figure	9.
19

Figure	13.	(A)	The	central	section	of	UAVSAR	line	13300	(Fig.	12)	showing	the	greatest	subsidence.	

(B)	The	one	area	that	showed	significant	subsidence	(outlined in	A),		with	up	to	5”	on	the	sides	of	

the	aqueduct. (C)	North	end	of	line	13300,	near	Buttonwillow.		The	only	high	subsidence	in	this	

area	occurs	near	oil	fields	(circled)	and	does	not	impact	the	aqueduct.

Conclusions and	Future Plans

PALSAR	and	Radarsat-2	have proved	to	be	useful	for	making	maps	of	Central Valley	

subsidence.	Maps	as	well	as	pixel	histories	of	subsidence	and	transects	showing	temporal	

and	spatial	details of	subsidence	can	be	produced	from	the	InSAR	data.	Updates	of	the	

subsidence	maps	for	the	Central	Valley	will	continue	with	the	advent	of	Europe’s	Sentinel1A	(Table	1).	The	first	acquisitions	for	the	Central	Valley	were	in	January	2015	and	are	

continuing,	in	general	every	24	days.	Figure	14 shows	example	coverage	of	Sentinel-1A.	

The	UAVSAR	results	show	that	radar	remote	sensing	using	high	resolution,	L-band (10”	

wavelength) SAR	can	rapidly	identify	the	localized	areas	of	subsidence,	so	that	resources	

can	be	targeted	efficiently	to	protect	and	maintain	critical	infrastructure. Using	UAVSAR,	
20

we	were	able	to	locate	and	monitor	a	previously	unknown	locus	of	subsidence	that	caused	

the	California	Aqueduct	to	subside	by	as	much	as	13”,	so	that	further	work	can	be	done	to	

identify	the	cause	of	the	subsidence	and	prevent	it	from	happening	in	the	future.

Furthermore,	with	frequent	monitoring	we	were	able	to	isolate	the	time	period	during	

which	rapid	subsidence	occurred.		Without	this	kind	of	comprehensive,	rapidly	acquired	

mapping	capability	it	would	not	be	possible	to	identify	through	ground	surveys	alone	this	

type	of	problem	that	rapidly	developed	during	the	ongoing	drought.	 UAVSAR	acquisitions	

of	the	two	swaths	imaging	the	California	Aqueduct	are	planned	to	continue	for	another	6-9	

months	at	least.	

As	described	above,	the	InSAR	time	series	we	produce	are	essentially	series	of	maps	

representing	the	change	in	surface	elevation	for	each	satellite	acquisition	date.	In	a	sense,	

we	produce 4-dimensional	data	sets.	We	have	found	a	convenient	format	for	storage	and	

post-processing	is	a	multi-band	GeoTiff	format,	where	each	‘band’	is	an	acquisition	date.	

Most	common	Geographic	Information	System	software	packages	recognize	this	format	

and	can	display	map	products	from	the	data.	We	will	furnish	all	of	our	products	to	the	DWR	

in	this	format	for	future	use	and	generation	of	additional	products.	

Figure	14.	Examples	of	Sentinel-1A	coverage	of	the	San	Joaquin	Valley.	All	of	California	will	be	

covered	by	this	satellite	approximately	every	24	days	from	both	ascending	(SE-NW)	and	

descending	(NE-SW)	tracks.	
21

Acknowledgements

This	work	was	funded	by	the	California	Department	of	Water	Resources.	Part	of	this	work	

was	carried	out	at	the	Jet	Propulsion	Laboratory,	California	Institute	of Technology,	under	

contract	with	NASA.	The	Alaska	Satellite	Facility	(http://www.asf.alaska.edu/)	archives	

and	distributes	the	PALSAR	data	used	in	this	study.	The	Japanese	Space	Agency contributed	

the	PALSAR	data.

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25

Appendix:			Detailed	lists of	data	used

Figure	A1. Map	showing	PALSAR	(white),	Radarsat-2 (green,	red,	purple), and	UAVSAR (blue)

coverage	of	the	Central	Valley.	Note	that	the	southern	edge	of	the	Radarsat-2	tracks (green) was	

determined	by	competing	data	acquisitions	by	oil	companies	monitoring	subsidence	in	the	oil	fields	

west	of	Bakersfield.	The	red	box	represents	the	San	Joaquin	Valley	frame	of	the	western	track	that	

is	not	shown	in	this	report.	
26

PALSAR Data	Listing

The	Phased-Array	L-band	Synthetic	Aperture	Radar	(PALSAR)	of	the	Japanese	Space	

Agency	(JAXA)	was	used	for	the	earlier	data	in	this	report.	Data	were	obtained	from	the	

Alaska	Satellite	Facility	(https://www.asf.alaska.edu).	See	Table	1	for	some	characteristics	

of	the	instrument.	Three	orbital	paths	were	used,	all	ascending	(SE	to	NW) and	shown	in	

Figure	A1:	2	to	cover the	San	Joaquin	Valley	and	1	for	the	southern	part	of	the	Sacramento	

Valley.	Swaths	are	broken	into	frames,	which	are	stitched	together	in	the	processing.	HH	

polarization	was	used	for	all	InSAR	products.	Details	of	the	frames	used	are	given	below.	

Table	A1.	Details	of	PALSAR	frames	used	for	this	report.	

Granule	Name Orbit Path Frame Acquisition	Date Center	Lat Center	Lon Angle

San	Joaquin	Valley,	East	swath

ALPSRP074860690 7486 218 690 6/21/07	6:26 35.1596 -119.4419 34.3

ALPSRP074860700 7486 218 700 6/21/07	6:26 35.6542 -119.5492 34.3

ALPSRP074860710 7486 218 710 6/21/07	6:26 36.1486 -119.6569 34.3

ALPSRP074860720 7486 218 720 6/21/07	6:26 36.6431 -119.7657 34.3

ALPSRP074860730 7486 218 730 6/21/07	6:26 37.1376 -119.8732 34.3

ALPSRP088280690 8828 218 690 9/21/07	6:26 35.1623 -119.4405 34.3

ALPSRP088280700 8828 218 700 9/21/07	6:26 35.6568 -119.5488 34.3

ALPSRP088280710 8828 218 710 9/21/07	6:26 36.1472 -119.6537 34.3

ALPSRP088280720 8828 218 720 9/21/07	6:26 36.6421 -119.7619 34.3

ALPSRP088280730 8828 218 730 9/21/07	6:26 37.1363 -119.8705 34.3

ALPSRP094990690 9499 218 690 11/6/07	6:25 35.1617 -119.4337 34.3

ALPSRP094990700 9499 218 700 11/6/07	6:25 35.6566 -119.5399 34.3

ALPSRP094990710 9499 218 710 11/6/07	6:25 36.1512 -119.6462 34.3

ALPSRP094990720 9499 218 720 11/6/07	6:26 36.6461 -119.7529 34.3

ALPSRP094990730 9499 218 730 11/6/07	6:26 37.1406 -119.8619 34.3

ALPSRP101700690 10170 218 690 12/22/07	6:25 35.1585 -119.4356 34.3

ALPSRP101700700 10170 218 700 12/22/07	6:25 35.6533 -119.5415 34.3

ALPSRP101700710 10170 218 710 12/22/07	6:25 36.1481 -119.6479 34.3

ALPSRP101700720 10170 218 720 12/22/07	6:25 36.6429 -119.7548 34.3

ALPSRP101700730 10170 218 730 12/22/07	6:25 37.1376 -119.8619 34.3

ALPSRP108410690 10841 218 690 2/6/08	6:24 35.1452 -119.424 34.3

ALPSRP108410700 10841 218 700 2/6/08	6:24 35.6401 -119.5294 34.3

ALPSRP108410710 10841 218 710 2/6/08	6:25 36.1348 -119.6358 34.3

ALPSRP108410720 10841 218 720 2/6/08	6:25 36.6296 -119.7424 34.3

ALPSRP108410730 10841 218 730 2/6/08	6:25 37.124 -119.8496 34.3

ALPSRP115120690 11512 218 690 3/23/08	6:24 35.1622 -119.4257 34.3

ALPSRP115120700 11512 218 700 3/23/08	6:24 35.6571 -119.5324 34.3

ALPSRP115120710 11512 218 710 3/23/08	6:24 36.1516 -119.6384 34.3

ALPSRP115120720 11512 218 720 3/23/08	6:24 36.6465 -119.7451 34.3

ALPSRP115120730 11512 218 730 3/23/08	6:24 37.1408 -119.8525 34.3

ALPSRP121830690 12183 218 690 5/8/08	6:23 35.1633 -119.4195 34.3

ALPSRP121830700 12183 218 700 5/8/08	6:23 35.6581 -119.5264 34.3

ALPSRP121830710 12183 218 710 5/8/08	6:23 36.1531 -119.6324 34.3

ALPSRP121830720 12183 218 720 5/8/08	6:23 36.6475 -119.7391 34.3

ALPSRP121830730 12183 218 730 5/8/08	6:23 37.142 -119.8461 34.3

ALPSRP128540690 12854 218 690 6/23/08	6:22 35.1462 -119.4407 34.3

ALPSRP128540700 12854 218 700 6/23/08	6:22 35.6408 -119.548 34.3
27

ALPSRP128540710 12854 218 710 6/23/08	6:23 36.1353 -119.656 34.3

ALPSRP128540720 12854 218 720 6/23/08	6:23 36.6299 -119.7628 34.3

ALPSRP128540730 12854 218 730 6/23/08	6:23 37.1241 -119.8719 34.3

ALPSRP135250690 13525 218 690 8/8/08	6:23 35.1617 -119.4842 34.3

ALPSRP135250700 13525 218 700 8/8/08	6:23 35.6563 -119.5923 34.3

ALPSRP135250710 13525 218 710 8/8/08	6:23 36.1507 -119.7007 34.3

ALPSRP135250720 13525 218 720 8/8/08	6:23 36.6453 -119.8085 34.3

ALPSRP135250730 13525 218 730 8/8/08	6:23 37.14 -119.9166 34.3

ALPSRP182220690 18222 218 690 6/26/09	6:27 35.1638 -119.456 34.3

ALPSRP182220700 18222 218 700 6/26/09	6:27 35.6585 -119.5623 34.3

ALPSRP182220710 18222 218 710 6/26/09	6:27 36.1533 -119.669 34.3

ALPSRP182220720 18222 218 720 6/26/09	6:27 36.6481 -119.7759 34.3

ALPSRP182220730 18222 218 730 6/26/09	6:27 37.1426 -119.8842 34.3

ALPSRP195640690 19564 218 690 9/26/09	6:27 35.16 -119.4506 34.3

ALPSRP195640700 19564 218 700 9/26/09	6:28 35.6551 -119.5569 34.3

ALPSRP195640710 19564 218 710 9/26/09	6:28 36.1495 -119.6636 34.3

ALPSRP195640720 19564 218 720 9/26/09	6:28 36.6443 -119.771 34.3

ALPSRP195640730 19564 218 730 9/26/09	6:28 37.1386 -119.8799 34.3

ALPSRP209060690 20906 218 690 12/27/09	6:27 35.156 -119.4426 34.3

ALPSRP209060700 20906 218 700 12/27/09	6:28 35.6508 -119.5485 34.3

ALPSRP209060710 20906 218 710 12/27/09	6:28 36.1453 -119.6565 34.3

ALPSRP209060720 20906 218 720 12/27/09	6:28 36.6399 -119.7648 34.3

ALPSRP209060730 20906 218 730 12/27/09	6:28 37.1343 -119.8725 34.3

ALPSRP222480690 22248 218 690 3/29/10	6:27 35.1356 -119.4289 34.3

ALPSRP222480700 22248 218 700 3/29/10	6:27 35.6301 -119.5359 34.3

ALPSRP222480710 22248 218 710 3/29/10	6:27 36.1248 -119.6435 34.3

ALPSRP222480720 22248 218 720 3/29/10	6:27 36.6193 -119.7505 34.3

ALPSRP222480730 22248 218 730 3/29/10	6:28 37.114 -119.8576 34.3

ALPSRP229190690 22919 218 690 5/14/10	6:27 35.1595 -119.4351 34.3

ALPSRP229190700 22919 218 700 5/14/10	6:27 35.6543 -119.541 34.3

ALPSRP229190710 22919 218 710 5/14/10	6:27 36.149 -119.6471 34.3

ALPSRP229190720 22919 218 720 5/14/10	6:27 36.6436 -119.7539 34.3

ALPSRP229190730 22919 218 730 5/14/10	6:27 37.1381 -119.8614 34.3

ALPSRP235900690 23590 218 690 6/29/10	6:26 35.1623 -119.4335 34.3

ALPSRP235900700 23590 218 700 6/29/10	6:26 35.6571 -119.5404 34.3

ALPSRP235900710 23590 218 710 6/29/10	6:26 36.1516 -119.6464 34.3

ALPSRP235900720 23590 218 720 6/29/10	6:27 36.6463 -119.7535 34.3

ALPSRP235900730 23590 218 730 6/29/10	6:27 37.1408 -119.8605 34.3

ALPSRP262740690 26274 218 690 12/30/10	6:23 35.1628 -119.4223 34.3

ALPSRP262740700 26274 218 700 12/30/10	6:24 35.658 -119.5281 34.3

ALPSRP262740710 26274 218 710 12/30/10	6:24 36.1525 -119.6341 34.3

ALPSRP262740720 26274 218 720 12/30/10	6:24 36.6471 -119.7404 34.3

ALPSRP262740730 26274 218 730 12/30/10	6:24 37.1419 -119.8478 34.3

San	Joaquin	Valley,	Center	swath

ALPSRP077340710 7734 219 710 7/8/07	6:28 36.1438 -120.1903 34.3

ALPSRP077340720 7734 219 720 7/8/07	6:28 36.6383 -120.2975 34.3

ALPSRP077340730 7734 219 730 7/8/07	6:28 37.1326 -120.4049 34.3

ALPSRP084050710 8405 219 710 8/23/07	6:28 36.1498 -120.1903 34.3

ALPSRP084050720 8405 219 720 8/23/07	6:28 36.6442 -120.2972 34.3

ALPSRP084050730 8405 219 730 8/23/07	6:28 37.139 -120.4046 34.3

ALPSRP097470710 9747 219 710 11/23/07	6:27 36.1511 -120.1839 34.3
28

ALPSRP097470720 9747 219 720 11/23/07	6:28 36.6456 -120.2909 34.3

ALPSRP097470730 9747 219 730 11/23/07	6:28 37.1396 -120.3999 34.3

ALPSRP104180710 10418 219 710 1/8/08	6:27 36.1413 -120.181 34.3

ALPSRP104180720 10418 219 720 1/8/08	6:27 36.6361 -120.2879 34.3

ALPSRP104180730 10418 219 730 1/8/08	6:27 37.1306 -120.3949 34.3

ALPSRP110890710 11089 219 710 2/23/08	6:26 36.151 -120.1721 34.3

ALPSRP110890720 11089 219 720 2/23/08	6:27 36.6458 -120.2785 34.3

ALPSRP110890730 11089 219 730 2/23/08	6:27 37.1406 -120.3872 34.3

ALPSRP117600710 11760 219 710 4/9/08	6:26 36.1285 -120.1621 34.3

ALPSRP117600720 11760 219 720 4/9/08	6:26 36.6231 -120.2689 34.3

ALPSRP117600730 11760 219 730 4/9/08	6:26 37.1177 -120.3762 34.3

ALPSRP124310710 12431 219 710 5/25/08	6:25 36.1481 -120.1694 34.3

ALPSRP124310720 12431 219 720 5/25/08	6:25 36.6425 -120.2761 34.3

ALPSRP124310730 12431 219 730 5/25/08	6:25 37.1371 -120.3834 34.3

ALPSRP131020710 13102 219 710 7/10/08	6:25 36.1508 -120.2045 34.3

ALPSRP131020720 13102 219 720 7/10/08	6:25 36.6451 -120.3129 34.3

ALPSRP131020730 13102 219 730 7/10/08	6:25 37.1393 -120.422 34.3

ALPSRP164570710 16457 219 710 2/25/09	6:28 36.1436 -120.2129 34.3

ALPSRP164570720 16457 219 720 2/25/09	6:29 36.6382 -120.3202 34.3

ALPSRP164570730 16457 219 730 2/25/09	6:29 37.1326 -120.4297 34.3

ALPSRP171280710 17128 219 710 4/12/09	6:29 36.1441 -120.2029 34.3

ALPSRP171280720 17128 219 720 4/12/09	6:29 36.6389 -120.3098 34.3

ALPSRP171280730 17128 219 730 4/12/09	6:29 37.1331 -120.4194 34.3

ALPSRP198120710 19812 219 710 10/13/09	6:30 36.1382 -120.1937 34.3

ALPSRP198120720 19812 219 720 10/13/09	6:30 36.6325 -120.3021 34.3

ALPSRP198120730 19812 219 730 10/13/09	6:30 37.1266 -120.4124 34.3

ALPSRP211540710 21154 219 710 1/13/10	6:30 36.1448 -120.1908 34.3

ALPSRP211540720 21154 219 720 1/13/10	6:30 36.6396 -120.2979 34.3

ALPSRP211540730 21154 219 730 1/13/10	6:30 37.1338 -120.407 34.3

ALPSRP224960710 22496 219 710 4/15/10	6:29 36.1538 -120.1853 34.3

ALPSRP224960720 22496 219 720 4/15/10	6:29 36.6482 -120.2922 34.3

ALPSRP224960730 22496 219 730 4/15/10	6:30 37.1431 -120.3994 34.3

ALPSRP231670710 23167 219 710 5/31/10	6:29 36.1432 -120.1807 34.3

ALPSRP231670720 23167 219 720 5/31/10	6:29 36.6381 -120.2874 34.3

ALPSRP231670730 23167 219 730 5/31/10	6:29 37.1326 -120.3944 34.3

ALPSRP258510710 25851 219 710 12/1/10	6:26 36.1273 -120.169 34.3

ALPSRP258510720 25851 219 720 12/1/10	6:27 36.6221 -120.2754 34.3

ALPSRP258510730 25851 219 730 12/1/10	6:27 37.1165 -120.3836 34.3

Southern	Sacramento	Valley

ALPSRP048750760 4875 221 760 12/24/06	6:33 38.6236 -121.8327 34.3

ALPSRP048750770 4875 221 770 12/24/06	6:33 39.1176 -121.9427 34.3

ALPSRP048750780 4875 221 780 12/24/06	6:33 39.6116 -122.0537 34.3

ALPSRP048750790 4875 221 790 12/24/06	6:33 40.1057 -122.1647 34.3

ALPSRP062170760 6217 221 760 3/26/07	6:33 38.6226 -121.8129 34.3

ALPSRP062170770 6217 221 770 3/26/07	6:33 39.1168 -121.923 34.3

ALPSRP062170780 6217 221 780 3/26/07	6:33 39.6111 -122.0337 34.3

ALPSRP062170790 6217 221 790 3/26/07	6:34 40.1052 -122.1447 34.3

ALPSRP089010760 8901 221 760 9/26/07	6:33 38.6206 -121.8074 34.3

ALPSRP089010770 8901 221 770 9/26/07	6:33 39.1146 -121.9187 34.3

ALPSRP089010780 8901 221 780 9/26/07	6:33 39.6085 -122.0291 34.3

ALPSRP089010790 8901 221 790 9/26/07	6:33 40.1027 -122.1402 34.3
29

ALPSRP102430760 10243 221 760 12/27/07	6:32 38.6228 -121.803 34.3

ALPSRP102430770 10243 221 770 12/27/07	6:32 39.1171 -121.9127 34.3

ALPSRP102430780 10243 221 780 12/27/07	6:32 39.6111 -122.0227 34.3

ALPSRP102430790 10243 221 790 12/27/07	6:33 40.1051 -122.1339 34.3

ALPSRP109140760 10914 221 760 2/11/08	6:32 38.6216 -121.7892 34.3

ALPSRP115850760 11585 221 760 3/28/08	6:31 38.6229 -121.7873 34.3

ALPSRP115850770 11585 221 770 3/28/08	6:31 39.1171 -121.8964 34.3

ALPSRP115850780 11585 221 780 3/28/08	6:31 39.6111 -122.0067 34.3

ALPSRP115850790 11585 221 790 3/28/08	6:31 40.1052 -122.1172 34.3

ALPSRP122560760 12256 221 760 5/13/08	6:30 38.3944 -121.7402 34.3

ALPSRP122560770 12256 221 770 5/13/08	6:30 38.8894 -121.8487 34.3

ALPSRP122560780 12256 221 780 5/13/08	6:30 39.3851 -121.9588 34.3

ALPSRP122560790 12256 221 790 5/13/08	6:31 39.8814 -122.072 34.3

ALPSRP149400760 14940 221 760 11/13/08	6:32 38.6226 -121.8397 34.3

ALPSRP149400770 14940 221 770 11/13/08	6:32 39.1165 -121.9501 34.3

ALPSRP149400780 14940 221 780 11/13/08	6:32 39.6107 -122.0615 34.3

ALPSRP149400790 14940 221 790 11/13/08	6:32 40.1047 -122.1732 34.3

ALPSRP156110760 15611 221 760 12/29/08	6:33 38.6233 -121.8382 34.3

ALPSRP156110770 15611 221 770 12/29/08	6:33 39.1176 -121.9487 34.3

ALPSRP156110780 15611 221 780 12/29/08	6:33 39.6106 -122.0622 34.3

ALPSRP156110790 15611 221 790 12/29/08	6:33 40.1046 -122.1744 34.3

ALPSRP169530760 16953 221 760 3/31/09	6:34 38.6096 -121.8247 34.3

ALPSRP182950760 18295 221 760 7/1/09	6:34 38.6195 -121.8251 34.3

ALPSRP182950770 18295 221 770 7/1/09	6:35 39.1136 -121.9352 34.3

ALPSRP182950780 18295 221 780 7/1/09	6:35 39.6076 -122.0459 34.3

ALPSRP182950790 18295 221 790 7/1/09	6:35 40.1017 -122.1577 34.3

ALPSRP196370760 19637 221 760 10/1/09	6:35 38.6246 -121.8177 34.3

ALPSRP196370770 19637 221 770 10/1/09	6:35 39.1186 -121.9279 34.3

ALPSRP196370780 19637 221 780 10/1/09	6:35 39.6126 -122.0387 34.3

ALPSRP196370790 19637 221 790 10/1/09	6:35 40.1067 -122.1497 34.3

ALPSRP209790760 20979 221 760 1/1/10	6:35 38.6206 -121.8099 34.3

ALPSRP209790770 20979 221 770 1/1/10	6:35 39.1148 -121.92 34.3

ALPSRP209790780 20979 221 780 1/1/10	6:35 39.6091 -122.0307 34.3

ALPSRP209790790 20979 221 790 1/1/10	6:35 40.1032 -122.1417 34.3

ALPSRP229920760 22992 221 760 5/19/10	6:34 38.6068 -121.7945 34.3

ALPSRP229920770 22992 221 770 5/19/10	6:34 39.1011 -121.9042 34.3

ALPSRP229920780 22992 221 780 5/19/10	6:34 39.5951 -122.0159 34.3

ALPSRP229920790 22992 221 790 5/19/10	6:34 40.0892 -122.1282 34.3

ALPSRP236630760 23663 221 760 7/4/10	6:33 38.6218 -121.796 34.3

ALPSRP236630770 23663 221 770 7/4/10	6:34 39.1161 -121.9054 34.3

ALPSRP236630780 23663 221 780 7/4/10	6:34 39.6101 -122.0157 34.3

ALPSRP236630790 23663 221 790 7/4/10	6:34 40.1042 -122.1267 34.3

ALPSRP243340780 24334 221 780 8/19/10	6:33 39.6121 -122.0147 34.3

ALPSRP243340790 24334 221 790 8/19/10	6:33 40.1061 -122.1259 34.3

ALPSRP256760760 25676 221 760 11/19/10	6:32 38.6221 -121.7922 34.3

ALPSRP256760770 25676 221 770 11/19/10	6:32 39.1164 -121.9018 34.3

ALPSRP256760780 25676 221 780 11/19/10	6:32 39.6109 -122.0123 34.3

ALPSRP256760790 25676 221 790 11/19/10	6:32 40.1048 -122.123 34.3
30

Radarsat-2 Data	Listing

The	Radarsat-2	satellite	(Table	1)	provided	the	more	recent	satellite	data	used	for	this	

report.	Radarsat-2	is	the	second	radar	satellite	launched	by	the	Canadian	Space	Agency.	It	

is	in	a	polar	orbit	which	allows	it	to	view	any	point	on	the	globe	every	24	days	(its	

minimum	repeat	period	for	subsidence	detection).	It	uses	a	wavelength	of	about	2”,	which	

makes	it	more	sensitive	than	longer-wavelength	radar	systems	to	disturbances	of	the	

ground	that	can	spoil	the	phase	information.	Spatial	resolution	is	typically	around	50-100	

feet,	but	during	InSAR	processing,	we	usually	average	to	about	300’	to	decrease	noise.	

For	this	study,	we	purchased	Radarsat-2	data	for	2	orbital	tracks,	covering	most	of	the	San	

Joaquin	Valley	and	the	southern	part	of	the	Sacramento	Valley	(Fig.	A1).	Tracks	are	cut	up	

into	frames;	2	frames	were	acquired	for	the	eastern	track	covering	the	eastern	part	of	the	

San	Joaquin	Valley	and	1	frame	was	acquired	for	the	western	track	covering	the	western	

side	of	the	San	Joaquin	Valley,	with	an	additional	frame	on	the	same	track	covering	the	

southern	part	of	the	Sacramento	Valley.	Dates	and	frame	ID	numbers	are	listed	below.

By	working	with	the	Canadian	Space	Agency,	we	acquired	6	dates	of	coverage	for	the	

eastern	track	and	9	dates	for	the	western	track	.	For	the	eastern	track,	we	obtained	

coverage	on	3	May	2014,	27	May	2014,	18	October	2014,	11	November	2014,	5	December	

2014,	and	22	January	2015.	The	gap	between	May	and	October	was	caused	by	a	

miscommunication	so	that	satellite	acquisition	was	stopped	during	that	time.	The	southern	

boundary	of	the	eastern	track	was	determined	due	to	the	competing	data	acquisitions	in	a	

different	data	mode	by	oil	companies	monitoring	subsidence	in	the	oil	fields	west	of	

Bakersfield.	For	the	western	track,	including	the	west	side	of	the	San	Joaquin	Valley	and	the	

southern	part	of	the	Sacramento	Valley,	we	obtained	SAR	coverage	from	20	May	2014	to	28	

November	2014.	

As	we	processed	the	data	for	the	eastern	track,	we	realized	that	the	5	December	2014	

acquisition	had	problems	with	the	data.	Missing	lines	were	detected	and	the	

interferograms	associated	with	that	date	are	distinctly	different	from	other	interferometric	

pairs.	For	this	reason,	we	excluded	that	date	from	our	processing	and	present	results	from	

the	remaining	5 dates	from	that	track.	The	subsidence	map	derived	from	the	western	track	

for	the	San	Joaquin	Valley	showed	the	same	subsidence	features	as	the	eastern	track,	so	we	

used	it	as	a	validation	for	the	eastern	result,	but	don’t	show	the	map	here.	

A	detailed	listing	of	all	Radarsat-2	data	used	for	this	report	is	given	in	Table	A2 below.	

Orbits	are	all	ascending	(SE	– NW),	Beam	mode	is	Fine	resolution,	Wide-swath	mode.	

Polarization	is	HH.	Data	were	purchased	from	MDA	Geospatial	Services	Inc.	through	

Resource	Strategies	Inc.	
31

Table	A2.	Listing	of	all	Radarsat-2	data	used	in	this	report.	

Date Time Orbit

Abs.	

Orbit Beam Pol.	 Angle Center	Lat/Lon

San	Joaquin	Valley- East

5/3/14 1:57:27 96-157A 33321.1 F0W2 HH 31.27 36°34'N/119°56'W

5/3/14 1:57:48 96-157A 33321.11 F0W2 HH 31.27 37°48'N/120°13'W

5/27/14 1:57:26 97-157A 33664.1 F0W2 HH 31.27 36°34'N/119°56'W

5/27/14 1:57:47 97-157A 33664.11 F0W2 HH 31.27 37°48'N/120°13'W

10/18/14 1:56:47 103-157A 35722.1 F0W2 HH 31.27 36°35'N/119°56'W

10/18/14 1:57:08 103-157A 35722.1 F0W2 HH 31.27 37°49'N/120°13'W

11/11/14 1:56:47 104-157A 36065.1 F0W2 HH 31.27 36°35'N/119°56'W

11/11/14 1:57:08 104-157A 36065.1 F0W2 HH 31.27 37°49'N/120°13'W

12/5/14 1:56:47 105-157A 36408.1 F0W2 HH 31.27 36°35'N/119°56'W

12/5/14 1:57:08 105-157A 36408.1 F0W2 HH 31.27 37°49'N/120°13'W

1/22/15 1:57:20 37094 F0W2 HH 31.27 36°36'N/119°56'W

1/22/15 1:57:40 37094 F0W2 HH 31.27 37°48'N/120°13'W

Sacramento	Valley

5/20/14 2:02:18 97-57A 33564.11 F0W2 HH 31.27 38°53'N/121°31'W

6/13/14 2:02:17 98-57A 33907.11 F0W2 HH 31.27 38°53'N/121°31'W

7/7/14 2:02:16 99-57A 34250.11 F0W2 HH 31.27 38°53'N/121°31'W

7/31/14 2:02:16 100-57A 34593.11 F0W2 HH 31.27 38°53'N/121°31'W

8/24/14 2:02:17 101-57A 34936.11 F0W2 HH 31.27 38°53'N/121°31'W

9/17/14 2:02:17 102-57A 35279.11 F0W2 HH 31.27 38°52'N/121°31'W

10/11/14 2:01:39 103-57A 35622.1 F0W2 HH 31.27 38°56'N/121°32'W

11/4/14 2:01:39 104-57A 35965.1 F0W2 HH 31.27 38°56'N/121°32'W

11/28/14 2:01:39 105-57A 36308.1 F0W2 HH 31.27 38°56'N/121°32'W

San	Joaquin	Valley- West

5/20/14 2:01:43 97-57A 33564.11 F0W2 HH 31.27 36°50'N/121°02'W

6/13/14 2:01:42 98-57A 33907.11 F0W2 HH 31.27 36°50'N/121°02'W

7/7/14 2:01:42 99-57A 34250.1 F0W2 HH 31.27 36°50'N/121°02'W

7/31/14 2:01:42 100-57A 34593.1 F0W2 HH 31.27 36°50'N/121°02'W

8/24/14 2:01:42 101-57A 34936.11 F0W2 HH 31.27 36°50'N/121°03'W

9/17/14 2:01:42 102-57A 35279.11 F0W2 HH 31.27 36°50'N/121°03'W

10/11/14 2:01:41 103-57A 35622.1 F0W2 HH 31.27 36°50'N/121°03'W

11/4/14 2:01:41 104-57A 35965.1 F0W2 HH 31.27 36°50'N/121°03'W

11/28/14 2:01:39 105-57A 36308.1 F0W2 HH 31.27 36°50'N/121°03'W

UAVSAR

The	two	UAVSAR	flight	lines	used	for	evaluating	subsidence	of	the	California	Aqueduct	

were	line	ID	CValle_13300	(southern	section)	and	line	ID	Snjoaq_14511	(northern	section).	

Table	A3 shows	the	flight	dates,	UAVSAR	flight	IDs,	and	temporal	baselines	for	lines 13300

and	14511.	Each	acquisition	was	used	in	at	least three interferograms	to	provide	sufficient	

redundancy	to	eliminate	systematic	effects	from	atmospheric	variation	and	aircraft	motion	

artifacts.		Acquisition	of	line	14511	began	earliest,	in	July	2013,	and	extended	through	
32

March	2015.		We	were	able	to	use	1-year	temporal	baseline,	same-season	interferograms	

with	this	data	set,	increasing	the	accuracy	of	small-scale	cumulative	subsidence	

measurements.		Acquisition	of	line	13300	began	in	April	2014	and	extended	through	

January	2015,	so	we	were	not	able	to	include	the	season-to-season	interferograms	in	that	

analysis.	Further	information	about	UAVSAR	can	be	found	at	http://uavsar.jpl.nasa.gov.	

Table	A3.	 UAVSAR	line	ID,	flight	ID,	and	acquisition	date	of	the	data	used	for	evaluating	subsidence	

of	the	California	Aqueduct	during	the	2014	drought.

UAVSAR Line ID 14511 UAVSAR Line ID 13300

Acq. 

No.

Flight 

ID

Date of 

acquisition 

Acq. 

No.

Flight ID Date of 

acquisition 

1 13129 7/19/2013 1 14033 4/2/2014

2 13165 10/31/2013 2 14062 5/15/2014

3 14005 1/17/2014 3 14086 6/16/2014

4 14019 2/12/2014 4 14112 8/14/2014

5 14033 4/2/2014 5 14140 10/6/2014

6 14068 5/29/2014 6 14166 11/13/2014

7 14086 6/16/2014 7 15002 1/7/2015

8 14112 8/14/2014

9 14140 10/6/2014

10 14166 11/13/2014

11 15002 1/7/2015

12 15017 3/10/2015

Figure	A2.	Graph	showing	the	pairs	of	images	used	to	form	interferograms	used	for	UAVSAR	line	ID	

13300	(left)	and	line	ID	14511	(right).		In	the	plot, the	bar	extends	from	the	date	of	acquisition	1	to	

the	date	of	acquisition	2.	

UAVSAR	uncertainties

Figures	A3 and	A4 show	the	uncertainties	associated	with	the	vertical	displacement	

(subsidence/uplift)	measurements.		These	uncertainties	cover	random	errors,	but	do	not	

include	systematic	errors,	i.e.,	systematic	shifts	that	affect	all	interferograms,	for	example,	

persistent	water	vapor	within	mountain	valleys,	were	it	present	in	all	images,	would	not	be	

included	in	the	error	estimation.		
33

Figure	A3.	Uncertainty	in	the	vertical	movement	derived	from	UAVSAR	line	ID	14511,	covering	the	

northern	section	of	the	California	Aqueduct	within	the	area	overseen	by	the	San	Luis	Field	Division.	
34

Figure	A4.	Uncertainty	in	the	subsidence	derived	from	UAVSAR	line	ID	13300,	covering	the	

southern	section	of	the	California	Aqueduct	within	the	area	overseen	by	the	San	Joaquin	Field	

Division.